Extensions for Distributed Authoring and Versioning on the World Wide Web

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          WEBDAV Working Group                     Y. Y. Goland, Microsoft
          INTERNET-DRAFT                 E. J. Whitehead, Jr., U.C. Irvine
          <draft-ietf-webdav-protocol-03>               A. Faizi, Netscape
                                                       S. R Carter, Novell
                                                         D. Jensen, Novell
          Expires April 6, 1998                         September 29, 1997


                   Extensions for Distributed Authoring and Versioning
                                        on the
                                World Wide Web -- WEBDAV


          Status of this Memo

          This document is an Internet-Draft. Internet-Drafts are working
          documents of the Internet Engineering Task Force (IETF), its
          areas, and its working groups. Note that other groups may also
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          Internet-Drafts are draft documents valid for a maximum of six
          months and may be updated, replaced, or made obsolete by other
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          Distribution of this document is unlimited. Please send comments
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          request@w3.org>.

          Discussions of the WEBDAV working group are archived at
          <URL:http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth>.


          Abstract

          This Document specifies a set of methods and content-types
          ancillary to HTTP/1.1 for the management of resource properties,
          simple name space manipulation, simple resource locking
          (collision avoidance) and resource version control.


                                  Table of Contents
          Abstract
          1    Terminology
          2    Data Model and Methods for DAV Properties
               2.1  Introduction
                    2.1.1 The DAV Property
                    2.1.2 Existing Metadata Proposals
                    2.1.3 Properties and HTTP Headers
               2.2  A Property Model for HTTP Resources
                    2.2.1 Overview
                    2.2.2 Property Namespace
               2.3  Schemas
                    2.3.1 PropSchema XML Element
                    2.3.2 DTD XML Element
                    2.3.3 DefinedProps XML Element






                    2.3.4 PropEntries XML Element
                    2.3.5 Live XML Element
               2.4  DAV Schema
                    2.4.1 DAV Property
                    2.4.2 Level XML Element
                    2.4.3 Prop XML element
                    2.4.4 PropLoc XML Attribute
                    2.4.5 Example
               2.5  Property Identifiers
                    2.5.1 Problem Definition
               2.6  Link XML Element
                    2.6.1 Problem Description
                    2.6.2 Solution Requirements
                    2.6.3 Link XML Element
                    2.6.4 Src XML Element
                    2.6.5 Dst XML Element
                    2.6.6 Example
               2.7  Multi-Status Response
                    2.7.1 Problem Definition
                    2.7.2 Solution Requirements
                    2.7.3 Multi-Status Response
               2.8  Properties and Methods
                    2.8.1 DELETE
                    2.8.2 GET
                    2.8.3 PROPPATCH
                    2.8.4 PUT
                    2.8.5 PROPFIND
          3    A Proposal for Collections of Web Resources and Name Space
          Operations
               3.1  Observations on the HTTP Object Model
                    3.1.1 Collection Resources
                    3.1.2 Creation and Retrieval of Collection Resources
                    3.1.3 Source Resources and Output Resources
               3.2  MKCOL Method
                    3.2.1 Problem Description
                    3.2.2 Solution Requirements
                    3.2.3 Request
                    3.2.4 Response
                    3.2.5 Example
               3.3  Standard DAV Properties
                    3.3.1 IsCollection Property
                    3.3.2 DisplayName Property
                    3.3.3 CreationDate Property
                    3.3.4 GETentity Property
                    3.3.5 INDEXentity Property
                    3.3.6 Content-Type XML Element
                    3.3.7 Content-Length XML Element
                    3.3.8 Content-Language XML Element
                    3.3.9 Last-Modified XML Element
                    3.3.10 Etag XML Element
               3.4  INDEX Method
                    3.4.1 Problem Description
                    3.4.2 Solution Requirements
                    3.4.3 The Request
                    3.4.4 The Response
                    3.4.5 ResInfo XML Element
                    3.4.6 Members XML Element
                    3.4.7 Href XML Element
                    3.4.8 Example
               3.5  Behavior of RFC 2068 Methods on Collections
                    3.5.1 GET, HEAD for Collections
                    3.5.2 POST for Collections
                    3.5.3 PUT for Collections
                    3.5.4 DELETE for Collections
                    3.5.5 DELETE Method for Non-Collection Resources






               3.6  COPY Method
                    3.6.1 Problem Description
                    3.6.2 Solution Requirements
                    3.6.3 The Request
                    3.6.4 The Response
                    3.6.5 Examples
               3.7  MOVE Method
                    3.7.1 Problem Description
                    3.7.2 Solution Requirements
                    3.7.3 The Request
                    3.7.4 The Response
                    3.7.5 Examples
               3.8  ADDREF Method
                    3.8.1 Problem Definition
                    3.8.2 Solution Requirements
                    3.8.3 The Request
                    3.8.4 Example
               3.9  DELREF Method
                    3.9.1 Problem Definition
                    3.9.2 Solution Requirements
                    3.9.3 The Request
                    3.9.4 Example
               3.10 PATCH Method
                    3.10.1 Problem Definition
                    3.10.2 Solution Requirements
                    3.10.3 The Request
                    3.10.4 text/xml elements for PATCH
                    3.10.5 The Response
                    3.10.6 Examples
               3.11 Headers
                    3.11.1 Destination Header
                    3.11.2 Enforce-Live-Properties Header
                    3.11.3 Overwrite Header
                    3.11.4 Destroy Header
                    3.11.5 Collection-Member Header
               3.12 Links
                    3.12.1 Source Link Property Type
          4    State Tokens
               4.1  Overview
                    4.1.1 Problem Description
                    4.1.2 Solution Requirements
               4.2  State Token Syntax
               4.3  State Token Conditional Headers
                    4.3.1 If-State-Match
                    4.3.2 If-None-State-Match
               4.4  State Token Header
               4.5  E-Tags
          5    Locking
               5.1  Problem Description - Overview
                    5.1.1 Exclusive Vs. Shared Locks
                    5.1.2 Required Support
               5.2  LOCK Method
                    5.2.1 Operation
                    5.2.2 Effect of Locks on Properties and Containers
                    5.2.3 Locking Replicated Resources
                    5.2.4 Interaction with other Methods
                    5.2.5 Lock Compatibility Table
                    5.2.6 Status Codes
                    5.2.7 Example
                    5.2.8 Lock-Info Request Header
                    5.2.9 Owner Request Header
                    5.2.10 Time-Out Header
                    5.2.11 State-Token Header
               5.3  Write Lock
               5.4  Lock Tokens





                    5.4.1 Problem Description
                    5.4.2 Proposed Solution
                    5.4.3 Lock Token Definition
               5.5  UNLOCK Method
                    5.5.1 Problem Definition
                    5.5.2 Example
               5.6  Discovery Mechanisms
                    5.6.1 Lock Type Discovery
                    5.6.2 Active Lock Discovery
          6    Version Control
          7    Internationalization Support
          8    Security Considerations
          9    Acknowledgements
          10   References
          11   Authors' Addresses



          1    Terminology

          Collection - A resource that contains member resources.

          Member Resource - a resource referred to by a collection. There
          are two types of member resources: external and internal.

          Internal Member Resource - the name given to a member resource of
          a collection whose URI is relative to the URI of the collection.

          External Member Resource - a member resource with an absolute URI
          that is not relative to its parentís URI.

          Properties - A set of name/value pairs that contain descriptive
          information about a resource.

          Live Properties - Properties whose semantics and syntax are
          enforced by the server. For example, a live "read-only" property
          that is enforced by the server would disallow PUTs to the
          associated resource.

          Dead properties - Properties whose semantics and syntax are not
          enforced by the server. A dead "read-only" property would not be
          enforced by the server and thus would not be used by the server
          as a reason to disallow a PUT on the associated resource.


          2    Data Model and Methods for DAV Properties

          2.1  Introduction


          2.1.1     The DAV Property

          Properties are pieces of data that describe the state of a
          resource. Properties are data about data. The term property is
          used within this specification to disambiguate the concept from
          the overloaded terms "metadata" and "attribute".
          Properties are used within distributed authoring environments to
          provide for efficient discovery and management of resources. For
          example, a 'subject' property might allow for the indexing of all
          resources by their subject, and an 'author' property might allow
          for the discovery of what authors have written which documents.


          2.1.2     Existing Metadata Proposals






          Properties have a long played an essential role in the
          maintenance of large document repositories, and many current
          proposals contain some notion of a property. These include PICS
          [Miller et al., 1996], PICS-NG, the Rel/Rev draft [Maloney,
          1996], Web Collections, XML [Bray, Sperberg-McQueen, 1997],
          several proposals on representing relationships within HTML,
          digital signature manifests (DCMF), and a position paper on Web
          metadata architecture [Berners-Lee, 1997].

          Some proposals come from a digital library perspective. These
          include the Dublin Core [Weibel et al., 1995] metadata set and
          the Warwick Framework [Lagoze, 1996], a container architecture
          for different metadata schemas. The literature includes many
          examples of metadata, including MARC [MARC, 1994], a
          bibliographic metadata format, RFC 1807 [Lasher, Cohen, 1995], a
          technical report bibliographic format employed by the Dienst
          system, and the proceedings from the first IEEE Metadata
          conference describe many community-specific metadata sets.

          Participants of the 1996 Metadata II Workshop in Warwick, UK
          [Lagoze, 1996], noted that, "new metadata sets will develop as
          the networked infrastructure matures" and "different communities
          will propose, design, and be responsible for different types of
          metadata." These observations can be corroborated by noting that
          many community-specific sets of metadata already exist, and there
          is significant motivation for the development of new forms of
          metadata as many communities increasingly make their data
          available in digital form, requiring a metadata format to assist
          data location and cataloging.


          2.1.3     Properties and HTTP Headers

          Properties already exist, in a limited sense, within HTTP through
          the use of message headers. However, in distributed authoring
          environments a relatively large number of properties are needed
          to describe the state of a resource, and setting/returning them
          all through HTTP headers is inefficient. Thus a mechanism is
          needed which allows a principal to identify a set of properties
          in which the principal is interested and to then set or retrieve
          just those properties.


          2.2  A Property Model for HTTP Resources


          2.2.1     Overview

          The DAV property model is based on name/value doubles. The name
          of a property identifies the property's syntax and semantics, and
          provides an address with which to refer to a property. The name
          and value of a property is expressed as a well-formed XML
          element, where the name of the property is the name of the XML
          element, and the value of the property MUST be either blank, or a
          well-formed XML element value.


          2.2.2     Property Namespace


          2.2.2.1   Problem Definition

          The requirement is to be able to associate a value with a
          property name on a resource and to be able to directly address
          that value.








          2.2.2.2   Solution Requirement

          Ideally a property namespace should work well with extant
          property implementations as well as database systems. The DAV
          property namespace has been specified with the following two
          facts in mind:
          ∑    Namespaces associated with flat file systems are ubiquitous.
          ∑    The majority of databases use a fixed schema mechanism.
          The last point makes efficient implementation of hierarchical
          properties difficult. Specifically, each property has a random
          set of children; the best a relational database can do is provide
          a table with name and value, where the value is a series of
          indexes into other tables and each index represents a specific
          value. However most RDBS do not provide for table pointers, only
          index values. Such a system would have to be jury-rigged to
          handle table pointers. In addition, indexing systems are
          optimized for a small set of relatively large tables;
          hierarchical property systems tend toward many properties, each
          with different numbers and types of children, thus potentially
          requiring a table for each child.

          It would seem best to implement a flat property namespace,
          inducing a natural isomorphism between DAV and most native file
          systems. Adopting such a model will not restrict RDBS from taking
          full advantage of their search facilities.

          However, it seems that future trends might be toward hierarchical
          properties. Therefore, DAV requirements [Slein et al.] stipulate
          that the design of the flat property system MUST be such that it
          will be possible to add true hierarchical properties later
          without breaking downlevel clients. Specifically, a flat client
          MUST be able to speak to a hierarchical server and a hierarchical
          client MUST be able to speak to a flat server. Worst case either
          way MUST be that the request fails.


          2.2.2.3   Property Names

          A property name identifies both the syntax and semantics of the
          property's value. It is critical that property names do not
          collide, e.g., two principals defining the same property name
          with two different meanings.

          The URI framework provides a mechanism to prevent namespace
          collision and for varying degrees of administrative control.
          Rather than reinvent these desirable features, DAV properties
          make use of them by requiring that all DAV property names MUST be
          URIs.  Since a property is also an XML element, the name of the
          XML element is a URI.

          The property namespace is flat, that is, it is not possible to
          string together a series of property names in order to refer to a
          hierarchy of properties. Thus it is possible to refer to a
          property B but not a property A/B, where is also a property
          defined on the resource.

          Finally, it is not possible to define the same property twice as
          this would cause a collision in the resource's property
          namespace.


          2.3  Schemas






          A schema is a group of property names and XML elements.

          Schema discovery is used to determine if a system supports a
          group of properties or XML elements. A property does not
          necessarily contain sufficient information to identify any
          schema(s) to which it may belong.

          As with property names, schemas MUST use URIs as their names.

          A resource declares its support for a schema by defining a
          property whose name is the same as the schema's. The property
          SHOULD contain the PropSchema XML element.


          2.3.1     PropSchema XML Element

          Name:     http://www.ietf.org/standards/dav/PropSchema
          Purpose:  To provide information about properties
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   [DTD] [DefinedProps]
          Description:This property contains the definition of the schema.
          This definition consists of two parts. A DTD element that
          contains a DTD that declares all XML elements and DefinedProps
          that defines any properties associated with the schema. As with
          all XML it is possible to add extra XML elements. Therefore
          schemas may define extra XML elements which are to be included
          with their values.

          2.3.2     DTD XML Element

          Name:          http://www.ietf.org/standards/dav/DTD
          Purpose:  To contain the DTD for XML elements associated with the
          schema.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values:   XML Declaration statements


          2.3.3     DefinedProps XML Element

          Name:          http://www.ietf.org/standards/dav/DefinedProps
          Purpose:  To contain a list of properties defined by the schema.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   1*PropEntries


          2.3.4     PropEntries XML Element

          Name:          http://www.ietf.org/standards/dav/PropEntries
          Purpose:  To contain the name of a defined property, the DTD of
          its value, and its live/dead status.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   DefinedProps
          Values=   Prop [DTD] [Live]
          Description:Prop contains the name of the property. The DTD
          contains the DTD of the property's value. Live, if defined,
          indicates that the property has semantics and syntax that are
          enforced by the server.


          2.3.5     Live XML Element

          Name:          http://www.ietf.org/standards/dav/Live






          Purpose:  If present this indicates the server MUST enforce the
          syntax and semantics of the property.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   PropEntries


          2.4  DAV Schema

          The DAV Schema is specified as
          http://www.ietf.org/standards/dav/. This schema is used to
          indicate support for
          ∑    properties that may be defined on a resource and
          ∑    XML elements that may be returned in responses.


          2.4.1     DAV Property

          Name:          http://www.ietf.org/standards/dav
          Purpose:  Defines support for the DAV schema and protocol.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   PropSchema Level
          Description:This property indicates that the resource supports
          the DAV schema and protocol to the level indicated. THE VALUE IN
          PROPSCHEMA IS TBD, WE NEED TO PROVIDE IT IN AN APPENDIX.


          2.4.2     Level XML Element

          Name:          http://www.ietf.org/standards/dav/level
          Purpose:  To indicate the level of DAV compliance the resource
          meets.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   DAV
          Values=   "1" | "2" | "3"
          Description:A value of 1 for level indicates that the resource
          supports the property and namespace sections of the DAV
          specification. Level 2 indicates that the resource supports level
          1 and the lock section of the specification, with a minimum
          locking capability of the write lock. Level 3 indicates support
          for levels 1 and 2 as well as support for the versioning section
          of the DAV specification.


          2.4.3     Prop XML element

          Name:          http://www.ietf.org/standards/dav/prop
          Purpose:  Contains properties related to a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values:   XML Elements
          Description:The Prop XML element is a generic container for
          properties defined on resources. All elements inside Prop MUST
          define properties related to the resource. No other elements may
          be used inside of a Prop element.


          2.4.4     PropLoc XML Attribute

          Name:          http://www.ietf.org/standards/dav/PropLoc
          Purpose:  To specify the location of the associated property.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   URL
          Description:This attribute is used with elements inside of Props
          contained in responses to specify the URL of the property on the
          associated resource. The PropLoc attribute MUST NOT be used in






          requests.


          2.4.5     Example

          <?XML:Namespace href="http://www.ietf.org/standards/dav/"
          AS="D"/>
          <?XML:Namespace href="AIIM:Dublin:" AS="A"/>
          <D:Prop>
               <A:Author
          D:PropLoc="http://www.foo.com/resource/props/Author">
                    Larry Masinter
               </A:Author>
          </D:Prop>

          The previous specifies that the property author exists on some
          unspecified resource and that the property can be directly
          referenced at http://www.foo.com/resource/props/Author. The
          resource upon which the property is defined must be determined
          from context.


          2.5  Property Identifiers


          2.5.1     Problem Definition

          DAV properties are resources and thus may have a URI where the
          value of an instance of the property may be retrieved.  This URI
          is separate from the URI name of the property, which identifies
          the syntax and semantics of the property, but which does not give
          information on how to access the value of an instance of the
          property.

          A server is free to assign whatever URI it chooses to identify an
          instance of a property defined on a resource. In fact, a server
          is free not to reveal the URI of an instance of a particular
          resource and instead require that the client access the property
          through PROPFIND and PROPPATCH.  However, many servers will want
          to allow clients to directly manipulate properties. On these
          servers, a client can discover the URI of an instance of a
          property by performing a PROPFIND and examining the PropLoc
          attribute, if returned, of each property.

          2.6  Link XML Element


          2.6.1     Problem Description

          A mechanism is needed to associate resources with other
          resources. These associations, known as links, consist of three
          values, a type describing the nature of the association, the
          source of the link, and the destination of the link. In the case
          of annotation, neither the source nor the destination of a link
          need be the resource upon which the link is recorded.


          2.6.2     Solution Requirements

          The association mechanism MUST make use of the DAV property
          mechanism in order to make the existence of the associations
          searchable.


          2.6.3     Link XML Element







          Name:          http://www.ietf.org/standards/dav/link
          Purpose:  To identify a property as a link and to contain the
          source and destination of that link.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   1*Src 1*Dst
          Description:Link is used to provide the sources and destinations
          of a link. The type of the property containing the Link XML
          element provides the type of the link. Link is a multi-valued
          element, so multiple Links may be used together to indicate
          multiple links with the same type.


          2.6.4     Src XML Element

          Name: http://www.ietf.org/standards/dav/src
          Purpose: To indicate the source of a link.
          Schema: http://www.ietf.org/standards/dav/
          Parent: http://www.ietf.org/standards/dav/link
          Values= URI


          2.6.5     Dst XML Element

          Name: http://www.ietf.org/standards/dav/Dst
          Purpose: To indicate the destination of a link
          Schema: http://www.ietf.org/standards/dav/
          Parent: http://www.ietf.org/standards/dav/link
          Values= URI


          2.6.6     Example

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.foocorp.com/Project/" AS = "F"/>
          <D:Prop>
               <Source>
                    <Link>
                         <F:ProjFiles>Source</F:ProjFiles>
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/main.c</dst>
                    </Link>
                    <Link>
                         <F:ProjFiles>Library</F:ProjFiles>
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/main.lib</dst>
                    </Link>
                    <Link>
                         <F:ProjFiles>Makefile</F:ProjFiles>
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/makefile</dst>
               <Link>
               </Source>
          </D:Prop>

          In this example the resource http://foo.bar/program has a source
          property defined which contains three links. Each link contains
          three elements, two of which, src and dst, are part of the DAV
          schema defined in this document, and one which is defined by the
          schema http://www.foocorp.com/project/ (Source, Library, and
          Makefile). A client which only implements the elements in the DAV
          spec will not understand the foocorp elements and will ignore
          them, thus seeing the expected source and destination links. An






          enhanced client may know about the foocorp elements and be able
          to present the user with additional information about the links.


          2.7  Multi-Status Response


          2.7.1     Problem Definition

          Some methods effect more than one resource. The effect of the
          method on each of the scoped resources may be different, as such
          a return format that can specify the effect of the method on each
          resource is needed.


          2.7.2     Solution Requirements

          The solution must:
          - communicate the status code and reason
          - give the URI of the resource on which the method was invoked
          -    be consistent with other return body formats
          -

          2.7.3     Multi-Status Response

          The default multi-status response body is an text/xml HTTP entity
          that contains a single XML element called multiresponse, which
          contains a set of XML elements called response, one for each 200,
          300, 400, and 500 series status code generated during the method
          invocation.  100 series status codes MUST NOT be recorded in a
          response XML element.


          2.7.3.1   MultiResponse

          Name: http://www.ietf.org/standards/dav/multiresponse
          Purpose:  Contains multiple response messages.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    1*Response [ResponseDescription]
          Description:The ResponseDescription at the top level is used to
          provide a general message describing the over arching nature of
          the response. If this value is available an application MAY use
          it instead of presenting the individual response descriptions
          contain within the responses.


          2.7.3.2   Response

          Name: http://www.ietf.org/standards/dav/response
          Purpose:  Holds a single response
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    (Prop | HREF) Status [ResponseDescription]
          Description: Prop MUST contain one or more empty XML elements
          representing the name of properties. Multiple properties may be
          included if the same response applies to them all. If HREF is
          used then the response refers to a problem with the referenced
          resource, not a property.


          2.7.3.3   Status

          Name: http://www.ietf.org/standards/dav/status
          Purpose:  Holds a single HTTP status-line






          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Response
          Value:    status-line   ;status-line defined in [Fielding et al.,
          1997]


          2.7.3.4   ResponseDescription

          Name:
          http://www.ietf.org/standards/dav/ResponseDescription
          Purpose:  Contains a message that can be displayed to the user
          explaining the nature of the response.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Multiresponse and/or Response
          Value:    Any
          Description:   This XML element provides information suitable to
          be presented to a user.


          2.8  Properties and Methods


          2.8.1     DELETE

          As properties are resources, the deletion of a property causes
          the same result as the deletion of any resource. It is worth
          pointing out that the deletion of a property effects both direct
          manipulation, that is by the property's URL, as well as indirect
          discovery and manipulation, that is PROPPATCH and PROPFIND.


          2.8.2     GET

          A GET with a Request-URI that identifies a property returns the
          name and value of that property.  Accept types may be used to
          specify the format of the return value, but all DAV compliant
          servers MUST at minimum support a return type of text/xml. If
          text/xml is used as the response format then it MUST return the
          name and value of the property using the Prop XML element.


          2.8.2.1   Example

          The following example assumes that the property's URL, originally
          generated by the server, was discovered by examining the proploc
          XML attribute returned on a result from a FINDPROP.

          GET /bar.html;prop=z39.50_authors HTTP/1.1
          Host: foo.com

          HTTP/1.1 200 OK
          Content-Type: text/xml
          Content-Length: xxxx
          E-tag: "1234"
          Last-Modified: xxxx

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.w3.com/standards/z39.50/"AS = "Z"/>
          <D:prop>
               <Z:Authors>
                    <Z:Author>Jane Doe</Z:Author>
                    <Z:Author>Joe Doe</Z:Author>
                     <Z:Author>Lots o'Doe</Z:Author>






               </Z:Authors>
          </D:prop>


          2.8.3     PROPPATCH

          The PROPPATCH method processes instructions specified in the
          request body to create and/or remove properties defined on the
          resource identified by Request-URI.

          All DAV compliant servers MUST process instructions which are
          specified using the PropertyUpdate, Create, and Remove XML
          elements of the DAV schema.  The request message body MUST
          contain at least one PropertyUpdate XML element.  Instruction
          processing MUST occur in the order instructions are received
          (i.e., from top to bottom), and MUST be performed atomically.


          2.8.3.1   PropertyUpdate XML element

          Name:          http://www.ietf.org/standards/dav/PropertyUpdate
          Purpose:  To contain a request to alter the properties on a
          resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   *(Create | Remove)
          Description:This XML element is a container for the information
          required to modify the properties on the resource. This XML
          element is multi-valued.


          2.8.3.2   Create XML element

          Name:          http://www.ietf.org/standards/dav/create
          Purpose:  To create the DAV properties specified inside the
          Create XML element.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   http://www.ietf.org/standards/dav/PropertyUpdate
          Values=   Prop
          Description:This XML element MUST contain only a Prop XML
          element. The elements contained by Prop specify the name and
          value of properties that are created on Request-URI. If a
          property already exists then its value is replaced. The Prop XML
          element MUST NOT contain a PropLoc XML attribute.


          2.8.3.3   Remove XML element

          Name:          http://www.ietf.org/standards/dav/remove
          Purpose:  To remove the DAV properties specified inside the
          Remove XML element.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   http://www.ietf.org/standards/dav/PropertyUpdate
          Values=   Prop
          Description:Remove specifies that the properties specified in
          Prop should be removed. Specifying the removal of a property that
          does not exist is not an error. All the elements in Prop MUST be
          empty, as only the names of properties to be removed are
          required.


          2.8.3.4   Response

          The response MUST have a response body that contains a
          multiresponse identifying the results for each property.








          2.8.3.5   Response Codes

          200 OK - The command succeeded. As there can be a mixture of
          Create and Removes in a body, a 201 Create seems inappropriate.
          403 Forbidden - The client, for reasons the server chooses not to
          specify, can not alter one of the properties.
          405 Conflict - The client has provided a value whose semantics
          are not appropriate for the property. This includes trying to set
          read only properties.
          413 Request Entity Too Long - If a particular property is too
          long to be recorded then a composite XML error will be returned
          indicating the offending property.
          417 Insufficient Space on Resource - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.
          418 Atomicity Failure - The command was not executed because of
          an atomicity failure elsewhere the caused the entire command to
          be aborted.


          2.8.3.6   Example

          PROPPATCH /bar.html HTTP/1.1
          Host: www.foo.com
          Content-Type: text/xml
          Content-Length: xxxx

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.w3.com/standards/z39.50/" AS = "Z"/>
          <D:PropertyUpdate>
               <Create>
                    <prop>
                         <Z:authors>
                              <Z:Author>Jim Whitehead</Z:Author>
                              <Z:Author>Roy Fielding</Z:Author>
                         </Z:authors>
                    </Prop>
               </Create>
               <Remove>
                    <prop><Z:Copyright-Owner/></prop>
               </Remove>
          </D:PropertyUpdate>

          HTTP/1.1 405 Conflict
          Content-Type: text/xml
          Content-Length: xxxxx

          <?XML:Namespace
               href="http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href="http://www.w3.com/standards/z39.50/" AS = "Z"/>
          <D:MultiResponse>
               <ResponseDescription> Copyright Owner can not be deleted or
          altered.</ResponseDescription>
               <Response>
                    <Prop><Z:authors/></Prop>
                    <Status>HTTP/1.1 418 Atomicity Failure</Status>
               </Response>
               <Response>
                    <Prop><Z:Copyright-Owner/></Prop>
                    <Status>HTTP/1.1 405 Conflict</Status>






               </Response>
          </D:MultiResponse>


          2.8.4     PUT

          A PUT is specified in order to control what is returned by a GET.
          However a GET on a property always returns a predefined property
          containment format. Therefore PUT can not be used if the Request-
          URI refers to a property.


          2.8.5     PROPFIND

          The PROPFIND method retrieves properties defined on Request-URI.
          The request message body is an XML document that MUST contain
          only one PropFind XML element, which specifies the type of
          property find action to be performed.  The XML element contained
          by PropFind specifies the type of action to be performed:
          retrieve all property names and values (AllProp), retrieve only
          specified property names and values (Prop), or retrieve only a
          list of all property names (Propname).  When a Prop XML element
          is present, it specifies a list of the names of properties whose
          name and value are to be returned.  The Prop element, when used
          within a FINDPROP request body MUST be empty.

          The response is a text/xml message body that contains a
          MultiResponse XML element which describes the results of the
          attempts to retrieve the various properties. If a property was
          successfully retrieved then its value MUST be returned in the
          prop XML element. In the case of Allprop and Findprop, if a
          principal does not have the right to know if a particular
          property exists, an error MUST NOT be returned. The results of
          this method SHOULD NOT be cached.


          2.8.5.1   Propfind XML element

          Name:          http://www.ietf.org/standards/dav/Propfind
          Purpose:  To specify the set of matching properties
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   (Prop | Allprop | Propname)
          Description: Propfind is a container element for the exact
          specification of a PROPFIND request.


          2.8.5.2   Allprop

          Name:          http://www.ietf.org/standards/dav/Allprop
          Purpose:  To specify that all properties are to be returned
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Propfind
          Description: Its presence in a PROPFIND request specifies the
          name and value of all properties defined on the resource MUST be
          returned.


          2.8.5.3   Propname

          Name:          http://www.ietf.org/standards/dav/Propname
          Purpose:  To specify that the names of all properties defined on
          the resource are to be returned.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Propfind






          Description: Its presence in a PROPFIND request specifies the
          name of all properties defined on the resource MUST be returned.


          2.8.5.4   PropFindResult XML element

          Name: http://www.ietf.org/standards/dav/PropFindResult
          Purpose: To contain the results of a SEARCH request
          Schema: http://www.ietf.org/standards/dav/
          Parent: Any
          Values: Prop


          2.8.5.5   Example 1 - Prop

          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml


          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "G"/>
          <?XML:Namespace href =
               "http://www.foo.bar/boxschema/" AS = "B"/>
          <G:PROPFIND>
               <prop>
                    <B:bigbox>
                    <B:author>
                    <B:DingALing>
                    <B:Random>
               </prop>
          </G:PROPFIND>

          HTTP/1.1 207 Partial Success
          Content-Type: text/xml
          Content-Length: xxxxx

          <?XML:Namespace
               href ="http://www.ietf.org/standards/dav/" AS = "S">
          <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
          <D:MultiResponse>
               <ResponseDescription> There has been an access violation
          error. </ResponseDescription>
               <Response>
                    <Prop>
                         <R:bigbox D:Proploc="http://prop.com/BoxType">
                              <BoxType>Box type A</BoxType>
                         </R:bigbox>
                         <R:author D:Proploc="http://prop.com/Author">
                              <Name>J.J. Dingleheimerschmidt</Name>
                         </R:author>
                    </Prop>
                    <Status>HTTP/1.1 200 Success</Status>
          </Response>
               <Response>
                    <Prop><R:DingALing/><R:Random/></>
                    <Status>HTTP/1.1 403 Forbidden</Status>
                    <ResponseDescription> The user does not have access to
          the DingALink property. </ResponseDescription>
               </Response>
          </D:MultiResponse>

          The result will return all properties on the container. In this
          case only two properties were found. The principal did not have






          sufficient access rights to see the third and fourth properties
          so an error was returned.


          2.8.5.6   Example 2 - Allprop

          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml

          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "G"/>
          <G:PROPFIND>
               <Allprop/>
          </G:PROPFIND>

          HTTP/1.1 200 Success
          Content-Type: text/xml
          Content-Length: xxxxx

          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" As = "S">
          <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
          <S:MultiResponse>
               <Prop>
                    <R:bigbox D:Proploc="http://prop.com/BigBox">
                         <BoxType>Box type A</BoxType>
                    </R:bigbox>
                    <R:author D:Proploc="http://prop.com/Author">
                         <Name>Hadrian</Name>
                    </R:author>
               </Prop>
               <Status>HTTP/1.1 200 Success</Status>
          </S:MultiResponse>

          This particular client only had the right to see two properties,
          BoxType and Author. No error is returned for the remaining
          properties, as the client does not even have sufficient rights to
          know they exist. If the client did have the right to know they
          existed but did not have the right to see their value, a 201
          Partial Success with a multiresponse, as used in the previous
          example, would have been returned.


          2.8.5.7   Example 3 - Propname

          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "G"/>
          <G:PROPFIND>
               <Propname/>
          </G:PROPFIND>

          HTTP/1.1 200 Success
          Content-Type: text/xml
          Content-Length: xxxxx

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" As = "S">
          <?XML:Namespace






               href = "http://www.foo.bar/boxschema" AS = "R">
          <S:MultiResponse>
               <Prop>
                    <R:bigbox D:Proploc="http://prop.com/BigBox"/>
                    <R:author D:Proploc="http://prop.com/Author"/>
                    <R:DingALing/>
                    <R:Random/>
               </Prop>
               <Status>HTTP/1.1 200 Success</Status>
          </S:MultiResponse>

          In this case only two of the properties have direct URLs
          available, while the other two properties can only be referenced
          via PROPFIND and PROPPATCH.


          3    A Proposal for Collections of Web Resources and Name Space
             Operations

          3.1  Observations on the HTTP Object Model

          This section provides a description of a new type of Web
          resource, the collection, and discusses its interactions with the
          HTTP URL namespace.  This discussion is a prerequisite for the
          specification of methods that operate on collections, given later
          in this document.


          3.1.1     Collection Resources

          A collection is a resource whose state consists of a list of
          internal members, a list of external members, and a set of
          properties.  An internal member resource MUST have a URI that is
          immediately relative to the base URI of the collection, that is,
          a relative URI in which "../" is illegal, which must begin with
          "./" and which MAY contain only one other "/" at the end of the
          URI. An external member resource MUST be an absolute URI that is
          not an internal URI.  Any given internal or external URI MUST
          only belong to the collection once, i.e., multiple instances of
          URIs in a collection are illegal.  Properties defined on
          collections have no special distinction, and behave exactly as do
          properties on non-collection resources.
          The purpose of a collection resource is to model collection-like
          objects (e.g., a filesystem directory) within a server's
          namespace.  Once these objects have been modeled with
          collections, a client may perform an INDEX, add and remove
          external members using ADDREF and DELREF, and perform recursive
          operations, such as a full hierarchy copy.
          To support methods which operate on collections, a server SHOULD
          model its collection-like objects with collection resources.  For
          example, a server which is implemented on top of a filesystem
          SHOULD treat all filesystem directories exposed by the server as
          collection resources.1


          3.1.2     Creation and Retrieval of Collection Resources

          This document specifies the MKCOL method to create new collection
          resources, and the INDEX method to list their contents.2
          In HTTP/1.1, the PUT method is defined to store the request body
          at the location specified by Request-URI.  While a description
          format for a collection can readily be constructed that could be
          used with PUT, the implications of sending such a description to
          the server are undesirable.  For example, if a description of a
          collection that omitted some existing resources were PUT to a






          server, this might be interpreted as a command to remove those
          members.  This would extend PUT to perform DELETE functionality,
          which is undesirable since it changes the semantics of PUT, and
          makes it difficult to control DELETE functionality with an access
          control scheme based on methods.
          While the POST method is sufficiently open-ended that a "create a
          collection" POST command could be constructed, this is
          undesirable because it would be difficult to separate access
          control for collection creation from other uses of POST if they
          both use the same method.
          While it might seem desirable to have GET return a listing of the
          members of a collection, this is foiled by the existence of the
          "index.html" de-facto standard namespace redirection, in which a
          GET request on a collection is automatically redirected to the
          index.html resource.
          The exact definition of the behavior of GET and PUT on
          collections is defined later in this document.


          3.1.2.1   Example

          The structured resource http://foo/bar is created with a PUT. Bar
          is a multipart/related file with two members http://foo/bar/a and
          http://foo/bar/b. If bar were deleted then both a and b would
          also be deleted since they are all really just one resource. If
          http://foo/bar/a/c was PUT then a DELETE on http://foo/bar/a
          would also delete http://foo/bar/a/c as c was created with a PUT
          not a MKCOL.
          If http://foo/bar/b/d is created with a MKCOL and
          http://foo/bar/b/d/e was created then a DELETE on d would fail
          because d is a collection with an internal member. However the
          existence of the collection d is something of an illusion. If a
          DELETE was executed on http://foo/bar then everything would be
          deleted, even though http://foo/bar/b/d was created with a MKCOL.
          Thus the effect of a MKCOL within a composite resourceís
          namespace is felt on its children, not its ancestors. The
          children of d MUST be treated as members of a collection when a
          method is executed on d. But a method executed on b or a is
          treated as if there only existed a non-collection resource.


          3.1.3     Source Resources and Output Resources

          For many resources, the entity returned by GET exactly matches
          the persistent state of the resource, for example, a GIF file
          stored on a disk.  For this simple case, the URL at which a
          resource is accessed is identical to the URL at which the source
          (the persistent state) of the resource is accessed. This is also
          the case for HTML source files that are not processed by the
          server prior to transmission.
          However, the server can sometimes process HTML resources before
          they are transmitted as a return entity body. For example,
          server-
          side-include directives within an HTML file instruct a server to
          replace the directive with another value, such as the current
          date.  In this case, what is returned by GET (HTML plus date)
          differs from the persistent state of the resource (HTML plus
          directive). Typically there is no way to access the HTML resource
          containing the unprocessed directive.
          Sometimes the entity returned by GET is the output of a data-
          producing process that is described by one or more source
          resources (that may not even have a location in the URL
          namespace).  A single data-producing process may dynamically
          generate the state of a potentially large number of output
          resources. An example of this is a CGI script that describes a






          "finger" gateway process that maps part of the namespace of a
          server into finger requests, such as
          http://www.foo.bar.org/finger_gateway/user@host.
          In the absence of distributed authoring capability, it is
          acceptable to have no mapping of source resource(s) to the URI
          namespace, and in fact has desirable security benefits. However,
          if remote editing of the source resource(s) is desired, the
          source resource(s) should be given a location in the URI
          namespace. This source location should not be one of the
          locations at which the generated output is retrievable, since in
          general it is impossible for the server to differentiate requests
          for source resources from requests for process output resources.
          There is often a many-to-many relationship between source
          resources and output resources.
          For DAV compliant servers all output resources which have a
          single source resource (and that source resource has a URI), the
          URI of the source resource SHOULD be stored in a single link on
          the output resource with type
          http://www.ietf.org/standards/dav/source. Note that by storing
          the source URI in links on the output resources, the burden of
          discovering the source is placed on the authoring client.


          3.2  MKCOL Method


          3.2.1     Problem Description

          A client must be able to create a collection.


          3.2.2     Solution Requirements

          The solution:
          -    Must ensure that a collection has been made (i.e. that it
            responds to the INDEX method) as opposed to a non-collection
            resource. If a collection could not be made, it must indicate
            this failure to the user-agent.


          3.2.3     Request

          MKCOL creates a new collection resource at the location specified
          by the Request-URI. If the Request-URI exists, then MKCOL must
          fail. During MKCOL processing, a server MUST make the Request-URI
          a member of its parent collection. If no such an ancestor exists,
          the method MUST fail. When the MKCOL operation creates a new
          collection resource, all ancestors MUST already exist, or the
          method MUST fail with a 409 Conflict status code.  For example,
          if a request to create collection /a/b/c/d/ is made, and neither
          /a/b/ nor /a/b/c/ exist, the request MUST fail.


          3.2.3.1   MKCOL Without Request Body

          When MKCOL is invoked without a request body, the newly created
          collection has no members.


          3.2.3.2   MKCOL With Request Body

          A MKCOL request message MAY contain a message body.  The behavior
          of a MKCOL request when the body is present is limited to
          creating collections, members of a collection, bodies of members
          and properties on the collections or members. If the server






          receives a MKCOL request entity type it does not support or
          understand it MUST respond with a 415 (Unsupported Media Type)
          status code.  The exact behavior of MKCOL for various request
          media types is undefined in this document, and will be specified
          in separate documents.


          3.2.4     Response

          Responses from a MKCOL request are not cacheable, since MKCOL has
          non-idempotent semantics.
          201 (Created) - The collection or structured resource was created
          in its entirety.
          403 (Forbidden) - This indicates at least one of two conditions:
          1) The server does not allow the creation of collections at the
          given location in its namespace, and 2) The parent collection of
          the Request-URI exists but cannot accept members.
          409 (Conflict) - A collection cannot be made at the Request-URI
          until one or more intermediate collections have been created.
          415 (Unsupported Media Type)- The server does not support the
          request type of the body.
          417 (Insufficient Space on Resource) - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.


          3.2.5     Example

          This example creates a container collection called
          /webdisc/xfiles/ on the server www.server.org.
               MKCOL /webdisc/xfiles/ HTTP/1.1
               Host: www.server.org


               HTTP/1.1 201 Created


          3.3  Standard DAV Properties

          The following properties are defined on DAV compliant resources.
          All enclosed properties are part of the DAV Schema.


          3.3.1     IsCollection Property

          Name:     http://www.ietf.org/standards/dav/iscollection
          Purpose:  This property contains a Boolean value that is set to
          "true" if the resource is a collection
          Schema:   http://www.ietf.org/standards/dav/
          Value:    ("true" | "false")
          Description: This property MUST be defined on all DAV compliant
          resources.


          3.3.2     DisplayName Property

          Name: http://www.ietf.org/standards/dav/displayname
          Purpose:  A name for the resource that is suitable for
          presentation to a user.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Any valid XML character data (as defined in [Bray,
          Sperberg-McQueen, 1997])
          Description: This property SHOULD be defined on all DAV compliant
          resources. If present, the property a description of the resource
          that is suitable for presentation to a user.








          3.3.3     CreationDate3 Property

          Name: http://www.ietf.org/standards/dav/creationdate
          Purpose:  The time and 4date the resource was created.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    The time and date MUST be given in ISO 8601 format
          [ISO8601]
          Description: This property SHOULD be defined on all DAV compliant
          resources. If present, it contains a timestamp of the moment when
          the resource was created (i.e., the moment it had non-null
          state).


          3.3.4     GETentity Property5

          Name: http://www.ietf.org/standards/dav/GETentity
          Purpose:  Contains the value of headers that are returned by a
          GET without Accept headers.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Content-Type Content-Length Content-Language Last-
          Modified Etag Creation-Date
          Description: This property MUST be defined on all DAV compliant
          resources unless GET is not supported, in which case this
          property MUST NOT be defined. This property MUST contain at most
          one instance of each element in its Value, if they are defined.

          3.3.5     INDEXentity Property

          Name: http://www.ietf.org/standards/dav/INDEXentity
          Purpose:  Contains the value of headers that are returned by an
          INDEX.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Content-Type Content-Length Content-Language Last-
          Modified Etag Creation-Date
          Description: This property MUST be defined on all DAV compliant
          resources unless INDEX is not supported, in which case this
          property MUST NOT be defined. This property MUST contain at most
          one instance of each element in its Value, if they are defined.


          3.3.6     Content-Type XML Element

          Name: http://www.ietf.org/standards/dav/content-type
          Purpose:  The content-type of the member resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   GETentity or INDEXentity
          Value:    media-type   ; defined in Section 3.7 of [Fielding et
          al., 1997]
          Description: If the parent of this element is GETentity, the
          value MUST be identical to the content-type returned by a GET on
          the resource without Accept headers.  If the parent is
          INDEXentity, the value MUST be identical to the content-type
          returned by an INDEX on the resource.  If no content-type is
          available, this element MUST NOT be defined.


          3.3.7     Content-Length XML Element

          Name:          http://www.ietf.org/standards/dav/content-length
          Purpose:  Describes the default content-length of the resource.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    content-length ; see section 14.14 of RFC 2068
          Description: If the parent of this element is GETentity, this






          element MUST have a value equal to the content-length header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the
          content-
          length returned by an INDEX on the resource.  If no content-
          length is available, this element MUST NOT be defined.


          3.3.8     Content-Language XML Element

          Name:          http://www.ietf.org/standards/dav/content-language
          Purpose:  Describes the default natural language of a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    language-tag   ;language-tag is defined in section
          14.13 of RFC 2068
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the content-language header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the
          content-
          language header returned by an INDEX on the resource.  If no
          content-language header is available, this element MUST NOT be
          defined.


          3.3.9     Last-Modified XML Element

          Name: http://www.ietf.org/standards/dav/last-modified
          Purpose:  The date the resource was last modified.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   GETentity or INDEXentity
          Value:    The date MUST be given in RFC 1123 format (rfc-1123
          production, defined in section 3.3.1 of [Fielding et al., 1997]
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the last-modified header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the last-
          modified header returned by an INDEX on the resource.  If no
          last-
          modified header is available, this element MUST NOT be defined.


          3.3.10    Etag XML Element

          Name: http://www.ietf.org/standards/dav/etag
          Purpose:  The entity tag of the resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   GETentity or INDEXentity
          Value:    entity-tag  ; defined in Section 3.11 of [Fielding et
          al., 1997]
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the entity-tag header returned
          by a GET on the resource without Accept headers.  If the parent
          is INDEXentity, the value MUST be identical to the entity-tag
          header returned by an INDEX on the resource.  If no entity-tag
          header is available, this element MUST NOT be defined.


          3.4  INDEX Method


          3.4.1     Problem Description

          A mechanism is needed to discover if a resource is a collection
          and if so, list its members.








          3.4.2     Solution Requirements

          The solution:
          -    must allow a client to discover the members of a collection
          -    must always provide a machine-readable description of the
            membership of a collection
          -    must be leveraged as a more general mechanism to provide a
            list of contents for any resource which can profitably return a
            membership like listing.


          3.4.3     The Request

          The INDEX method returns a machine-readable representation of the
          membership of the resource at the Request-URI. 6

          For a collection, INDEX MUST return a 7list of its members. All
          WebDAV compliant resources MUST support the text/xml response
          entity described below.  The INDEX result for a collection MAY
          also return a list of the members of child collections, to any
          depth.

          Collections that respond to an INDEX method with a text/xml
          entity MUST contain only one ResInfo element.  This ResInfo
          element contains an Href element, which gives the identifier(s)
          of the resource, a Prop element, which gives selected properties
          of the resource, and a Members element, which contains a ResInfo
          element for each member of the collection.  The Prop element MUST
          contain at least the following properties, if they are defined
          and available8: DisplayName, IsCollection, CreationDate,
          GETentity, and INDEXentity.

          The response from INDEX is cacheable, and SHOULD be accompanied
          by an ETag header (see section 13.3.4 of RFC 2068). If GET and
          INDEX return different entities for the same resource state, they
          MUST return different entity tags.


          3.4.4     The Response

          200 (OK) - The server MUST send a machine readable response
          entity which describes the membership of the resource.


          3.4.5     ResInfo XML Element

          Name:     http://www.ietf.org/standards/dav/resinfo
          Purpose:  Describes a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    Href Prop Members9
          Description: There MUST be at least one Href element.  Each Href
          element contains a URI for the resource, which MUST be an
          absolute URI. There MUST be a single Prop element that contains a
          series of properties defined on the resource.  If the resource is
          a collection, it MAY have at most one Members element, which
          describes the members of the collection.


          3.4.6     Members XML Element

          Name: http://www.ietf.org/standards/dav/members
          Purpose:  Describes the membership of a collection resource.






          Schema:   http://www.ietf.org/standards/dav/
          Parent:   ResInfo
          Value:    ResInfo
          Description: Contains zero or more ResInfo elements, which
          describe members of the collection.


          3.4.7     Href XML Element
          10
          Name: http://www.ietf.org/standards/dav/href
          Purpose:  To identify that the content of the element is a URI.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    URI ; See section 3.2.1 of [Fielding et al., 1997]

          3.4.8     Example

          INDEX /user/yarong/dav_drafts/ HTTP/1.1
          Host: www.microsoft.com

          HTTP/1.1 200 OK
          Content-Type: text/xml
          Content-Length: xxx
          Last-Modified: Thu, 11 Sep 1997 23:45:12 GMT
          ETag: "fooyyybar"

          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" as = "D"/>
          <D:ResInfo>
               <XML:Href>
                    http://www.microsoft.com/user/yarong/dav_drafts/
               </XML:Href>
               <Prop>
                  <DisplayName>
                    WebDAV working drafts directory
                  </DisplayName>
                  <IsCollection>true</IsCollection>
                  <CreationDate>19970418T070304Z</CreationDate>
                  <GETentity>
                    <Content-Type>text/html</Content-Type>
                    <Content-Length>2754</Content-Length>
                    <Content-Language>en</Content-Language>
                    <Last-Modified>
                         Fri, 22 Aug 1997 10:11:26 GMT
                    </Last-Modified>
                    <Etag>"8675309"</Etag>
                  </GETentity>
                  <INDEXentity>
                    <Content-Type>text/xml</Content-Type>
                    <Content-Length>xxx</Content-Length>
                    <Last-Modified>
                         Thu, 11 Sep 1997 23:45:12 GMT
                    </Last-Modified>
                    <Etag>"fooyyybar"</Etag>
                  </INDEXentity>
               </Prop>

               <Members>
                  <ResInfo>
                    <XML:Href>
                    http://www.microsoft.com/user/yarong/dav_drafts/base
                    </XML:Href>
                    <Prop>
                       <IsCollection
               D:PropLoc="http://www.microsoft.com/user/yarong/dav_drafts/b






               ase;props=IsCollection">
                         False
                       </IsCollection>
                       <DisplayName>
                         WebDAV Name Space Operations Draft
                       </DisplayName>
                       <Creation-Date>19970320T230525Z</Creation-Date>

                       <GETentity>
                         <Content-Type>application/msword</Content-Type>
                         <Content-Length>1400</Content-Length>
                         <Content-Language>en</Content-Language>
                         <Last-Modified>
                              Fri, 22 Aug 1997 18:22:56 GMT
                         </Last-Modified>
                         <Etag>"8675309"</Etag>
                       </GETentity>
                    </Prop>
                  </ResInfo>
               </Members>
          </D:ResInfo>
          This example shows the result of the INDEX method applied to the
          collection resource
          http://www.microsoft.com/user/yarong/dav_drafts/.  It returns a
          response body in XML format, which gives information about the
          container and its sole member,
          http://www.microsoft.com/user/yarong/dav_drafts/base. The entry
          on the collection confirms that resource the INDEX was executed
          on is a collection. The result also contains the URI of the
          IsCollection property on the member resource.


          3.5  Behavior of RFC 2068 Methods on Collections

          With the introduction of the collection resource type to the HTTP
          object model, it is necessary to define the behavior of the
          existing methods (defined in RFC 2068) when invoked on a
          collection resource to avoid ambiguity.  While some methods, such
          as OPTIONS and TRACE behave identically when applied to
          collections, GET, HEAD, POST, PUT, and DELETE require some
          additional explanation.


          3.5.1     GET, HEAD for Collections

          The semantics of GET are unchanged when applied to a collection,
          since GET is defined as, "retrieve whatever information (in the
          form of an entity) is identified by the Request-URI" [Fielding et
          al., 1997]. GET when applied to a collection MAY return the
          contents of an "index.html" resource, a human-readable view of
          the contents of the collection, or something else altogether, and
          hence it is possible the result of a GET on a collection will
          bear no correlation to the state of the collection.
          Similarly, since the definition of HEAD is a GET without a
          response message body, the semantics of HEAD are unmodified when
          applied to collection resources.


          3.5.2     POST for Collections

          Since by definition the actual function performed by POST is
          determined by the server and often depends on the particular
          resource, the behavior of POST when applied to collections cannot
          be meaningfully modified because it is largely undefined.  Thus
          the semantics of POST are unmodified when applied to a






          collection.


          3.5.3     PUT for Collections

          As defined in the HTTP/1.1 specification [Fielding et al., 1997],
          the "PUT method requests that the enclosed entity be stored under
          the supplied Request-URI."  Since submission of an entity
          representing a collection would implicitly encode creation and
          deletion of resources, this specification intentionally does not
          define a transmission format for creating a collection using PUT.
          Instead, the MKCOL method is defined to create collections.  If a
          PUT is invoked on a collection resource it MUST fail.
          When the PUT operation creates a new non-collection resource all
          ancestors MUST already exist.  If all ancestors do not exist, the
          method MUST fail with a 409 Conflict status code.  For example,
          if resource /a/b/c/d.html is to be created and /a/b/c/ does not
          exist, then the request MUST fail.


          3.5.3.1   PUT for Non-Collection Resources

          A PUT performed on an existing resource replaces the GET response
          entity of the resource, but MUST NOT change the value of any dead
          properties defined on the resource.  Live properties defined on
          the resource MAY be recomputed during PUT processing.


          3.5.4     DELETE for Collections

          When DELETE is applied to a collection without internal members
          the collection resource, along with its properties, and external
          members, MUST be deleted.  A DELETE method applied to a
          collection resource containing internal member resources MUST
          fail with a 409 Conflict status code1112.


          3.5.5     13DELETE Method for Non-Collection Resources

          If the DELETE method is issued to a non-collection resource which
          is an internal member of a collection, then during DELETE
          processing a server MUST remove the Request-URI from its parent
          collection. A server MAY remove the URI of a deleted resource
          from any collections of which the resource is an external member.


          3.6  COPY Method


          3.6.1     Problem Description

          Currently, in order to create a copy of a resource, the client
          must GET an entity and then PUT that entity to the desired
          destination. This requires (1) an entity to be transmitted to and
          from the server and (2) that the resource be expressible as an
          entity with complete fidelity.
          This is problematic because of the network traffic involved in
          making a copy, and because there is often no way to fully express
          a resource as an entity without a loss of fidelity.


          3.6.2     Solution Requirements

          The solution:
          -    MUST allow a principal to create a copy of a resource






          without having to transmit the resource to and from the server.


          3.6.3     The Request

          The COPY method creates a duplicate of the source resource, given
          by the Request-URI, in the destination resource, given by the
          Destination header.  The Destination header MUST be present.  The
          exact behavior of the COPY method depends on the type of the
          source resource.


          3.6.3.1   COPY for HTTP/1.1 resources

          When the source resource is not a collection, and is not a
          property, the body of the destination resource MUST be octet-for-
          octet identical to the body of the source resource. Alterations
          to the destination resource do not modify the source resource.
          Alterations to the source resource do not modify the destination
          resource. Thus, all copies are performed "by-value".
          All properties on the source resource MUST be duplicated on the
          destination resource, subject to modifying headers, following the
          definition for copying properties.


          3.6.3.2   COPY for Properties

          The following section defines how properties on a resource are
          handled during a COPY operation.
          Live properties SHOULD be duplicated as identically behaving live
          properties at the destination resource. Since they are live
          properties, the server determines the syntax and semantics (hence
          value) of these properties.  Properties named by the Enforce-
          Live-
          Properties header MUST be live on the destination resource, or
          the method MUST fail.  If a property is not named by Enforce-
          Live-
          Properties and cannot be copied live, then its value MUST be
          duplicated, octet-for-octet, in an identically named, dead
          resource on the destination resource.
          If a property on the source already exists on the resource and
          the overwrite header is set to TRUE then the property at the
          destination MUST be overwritten with the property from the
          source. If the overwrite header is false and the previous
          situation exists then the COPY MUST fail with a 409 Conflict.


          3.6.3.3   COPY for Collections

          A COPY on a collection causes a collection resource to be created
          at the destination with the same properties, but without any
          members, internal or external.  All properties on the source
          collection are copied over to the destination collection. Where
          there is a conflict the source properties will overwrite the
          destination properties. Any members at theMUST be duplicated on
          the destination collection, subject to modifying headers,
          following the definition for copying properties.


          3.6.3.4   Type Interactions

          If the destination resource identifies a property and the source
          resource is not a property, then the copy SHOULD fail.
          If the destination resource identifies a collection and the
          Overwrite header is "true," prior to performing the copy, the






          server MUST perform a DELETE operation on the collection.


          3.6.4     The Response

          200 (OK) The source resource was successfully copied to a pre-
          existing destination resource.
          201 (Created) The source resource was successfully copied.  The
          copy operation resulted in the creation of a new resource.
          412 (Precondition Failed) This status code MUST be returned if
          the server was unable to maintain the liveness of the properties
          listed in the Enforce-Live-Properties header, or if the Overwrite
          header is false, and the state of the destination resource is
          non-
          null.
          417 (Insufficient Space on Resource) - The destination resource
          does not have sufficient space to record the state of the
          resource after the execution of this method.
          500 (Server Error) The resource was in such a state that it could
          not be copied. This may occur if the Destination header specifies
          a resource that is outside the namespace the resource is able to
          interact with.


          3.6.5     Examples


          3.6.5.1   Overwrite Example

          This example shows resource
          http://www.ics.uci.edu/~fielding/index.html being copied to the
          location http://www.ics.uci.edu/users/f/fielding/index.html.  The
          contents of the destination resource were overwritten, if non-
          null.

          COPY /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html


          HTTP/1.1 200 OK


          3.6.5.2   No Overwrite Example

          The following example shows the same copy operation being
          performed, except with the Overwrite header set to "false."  A
          response of 412, Precondition Failed, is returned because the
          destination resource has a non-null state.

          COPY /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html
          Overwrite: "false"


          HTTP/1.1 412 Precondition Failed




          3.7  MOVE Method






          3.7.1     Problem Description

          The move operation on a resource is the logical equivalent of a
          copy followed by a delete, where the actions are performed
          atomically.  Using RFC 2068 methods only, this procedure could be
          performed in several steps. First, the client could issue a GET
          to retrieve a representation of a resource, issue a DELETE to
          remove the resource from the server, then use PUT to place the
          resource on the server with a new URI. As is the case for COPY -
          because of the network traffic involved in making a move, and
          because there is often no way to fully express a resource as an
          entity without a loss of fidelity - server move functionality is
          preferable.
          With a WEBDAV server, a principal may accomplish this task by
          issuing a COPY and then DELETE. Network load decreases, but the
          server load may still be significant because the server must
          create a duplicate resource. Were a server to know beforehand
          that a principal intended to perform COPY and DELETE operations
          in succession, it could avoid the creation of a duplicate
          resource.


          3.7.2     Solution Requirements

          The solution:
          -    Must prevent the unneeded transfer of entity bodies from and
            to the server.
          -    Must prevent the unneeded creation of copies by the server.


          3.7.3     The Request

          The move operation on a resource is the logical equivalent of a
          copy followed by a delete, where the actions are performed
          atomically. If a resource exists at the destination, the
          destination resource will be DELETEd as a side effect of the MOVE
          operation, subject to the restrictions of the overwrite header.


          3.7.4     The Response

          200 (OK) - The resource was moved. A successful response must
          contain the Content-Location header, set equal to the URI in
          source. This lets caches properly flush any cached entries for
          the source. Unfortunately the Content-Location header only allows
          a single value so it is not possible for caches unfamiliar with
          the MOVE method to properly clear their caches.
          412 (Precondition Failed) This status code MUST be returned if
          the server was unable to maintain the liveness of the properties
          listed in the Enforce-Live-Properties header, or if the Overwrite
          header is false, and the state of the destination resource is
          non-
          null.
          501 (Not Implemented) - This may occur if the Destination header
          specifies a resource which is outside its domain of control
          (e.g., stored on another server) resource and the server either
          refuses or is incapable of moving to an external resource.
          502 (Bad Gateway) - This may occur when moving to external
          resources and the destination server refused to accept the
          resource.


          3.7.5     Examples






          3.7.5.1   Overwrite Example

          This example shows resource
          http://www.ics.uci.edu/~fielding/index.html being moved to the
          location http://www.ics.uci.edu/users/f/fielding/index.html.  The
          contents of the destination resource were overwritten, if non-
          null.

          MOVE /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html


          HTTP/1.1 200 OK
          Content-Location:
          http://www.ics.uci.edu/users/f/fielding/index.html


          3.8  ADDREF Method


          3.8.1     Problem Definition

          There needs to be a way to add an external member to a
          collection.


          3.8.2     Solution Requirements

          The solution must:
          -    allow access control
          -    allow referencing to URIs of external members
          -    not require a body


          3.8.3     The Request

          The ADDREF method adds the URI specified in the Collection-Member
          header as an external member to the collection specified by the
          Request-URI. The value in the Collection-Member header MUST be an
          absolute URI meeting the requirements of an external member URI.
          It is not an error if the URI specified in the Collection-Member
          header already exists as an external member of the collection,
          however, after processing ADDREF there MUST be only one instance
          of the URI in the collection.  If the URI specified in the
          Collection-Member header already exists as an internal member of
          the collection, the ADDREF method MUST fail with a 412
          Precondition Failed status code.


          3.8.4     Example

          ADDREF /~whitehead/dav/ HTTP/1.1
          HOST: www.ics.udi.edu
          Collection-Member: http://www.ietf.org/standards/dav/


          HTTP/1.1 200 OK


          3.9  DELREF Method


          3.9.1     Problem Definition






          There needs to be a way to remove an external member from a
          collection.


          3.9.2     Solution Requirements

          The solution must:
          -    allow access control
          -    allow referencing to URIs of external members
          -    not require a body


          3.9.3     The Request

          The DELREF method removes the URI specified in the Collection-
          Member header from the collection specified by the Request-URI.
          DELREFing a URI which is not a member of the collection is not an
          error. DELREFing an internal member MUST fail with a 412
          Precondition Failed status code.


          3.9.4     Example

          DELREF /~whitehead/dav/ HTTP/1.1
          Host: www.ics.udi.edu
          Collection-Member: http://www.ietf.org/standards/dav/


          HTTP/1.1 200 OK


          3.10 PATCH Method


          3.10.1    Problem Definition

          At present, if a principal wishes to modify a resource, they must
          issue a GET against the resource, modify their local copy of the
          resource, and then issue a PUT to place the modified resource on
          the server. This procedure is inefficient because the entire
          entity for a resource must be transmitted to and from the server
          in order to make even small changes.  Ideally, the update entity
          transmitted to the server should be proportional in size to the
          modifications.


          3.10.2    Solution Requirements

          The solution must:
          -    allow partial modification of a resource without having to
            transmit the entire modified resource
          -    allow byte-range patching
          -    allows extensions so that patches can be done beyond simple
            byte-range patching
          -    allow ranges to be deleted, inserted, and replaced


          3.10.3    The Request

          The request entity of the PATCH method contains a list of
          differences between the resource identified by the Request-URI
          and the desired content of the resource after the PATCH action
          has been applied.  The list of differences is in a format defined
          by the media type of the entity (e.g., "application/diff") and
          must include sufficient information to allow the server to






          convert the original version of the resource to the desired
          version.  Processing performed by PATCH is atomic, hence all
          changes MUST be successfully executed or the method fails. PATCH
          MUST fail if executed on a non-existent resource; i.e. PATCH does
          not create a resource as a side effect.
          If the request appears (at least initially) to be acceptable, the
          server MUST transmit an interim 100 response message after
          receiving the empty line terminating the request headers and
          continue processing the request.  Since the semantics of PATCH
          are non-idempotent, responses to this method are not cacheable.
          While server support for PATCH is optional, if a server does
          support PATCH, it MUST support at least the text/xml diff format
          defined below.  Support for the VTML difference format [VTML] is
          recommended, but not required.


          3.10.4    text/xml elements for PATCH

          The resourceupdate XML element contains a set of XML sub-entities
          that describe modification operations.  The name and meaning of
          these XML elements is given below. Processing of these directives
          MUST be performed in the order encountered within the XML
          document.  A directive operates on the resource as modified by
          all previous directives (executed in sequential order). The
          length of the resource MAY be extended or reduced by a PATCH.
          The changes specified by the resourceupdate XML element MUST be
          executed atomically.


          3.10.4.1  ResourceUpdate

          Name:     http://www.ietf.org/standards/dav/patch/resourceupdate
          Purpose:       Contains an ordered set of changes to a non-
          collection, non-property resource.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        Any
          Value:         *(Insert | Delete | Replace)


          3.10.4.2  Insert

          Name:     http://www.ietf.org/standards/dav/patch/insert
          Purpose:       Insert the XML elementís contents starting at the
          specified octet.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The insert XML element MUST contain an Octet-Range
          XML element that specifies an octet position within the body of a
          resource.  A value of "end" specifies the end of the resource.
          The body of the insert XML element contains the octets to be
          inserted.
          Please note that in order to protect the white space contained in
          this XML element the following attribute/value MUST be included
          in the element: XML-SPACE = "PRESERVE".


          3.10.4.3  Delete

          Name:     http://www.ietf.org/standards/dav/patch/delete
          Purpose:       Removes the specified range of octets.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The Delete XML element MUST contain an octet-range
          XML element.
          Discussion: The octets that are deleted are removed, which means






          the resource is collapsed and the length of the resource is
          decremented by the size of the octet range.  It is not
          appropriate to replace deleted octets with zeroed-out octets,
          since zero is a valid octet value.


          3.10.4.4  Replace

          Name:     http://www.ietf.org/standards/dav/patch/replace
          Purpose:       Replaces the specified range of octets with the
          contents of the XML element.  If the number of octets in the XML
          element is different from the number of octets specified, the
          update MUST be rejected.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The Replace XML element MUST contain an octet-
          range XML element. The contents of the entity are the replacement
          octets.
          Please note that in order to protect the white space contained in
          this XML element the following attribute/value MUST be included
          in the element: XML-SPACE = "PRESERVE".


          3.10.4.5  Octet-Range Attribute

          Name:          http://www.ietf.org/standards/dav/patch/octet-
          range
          Purpose:  Specifies a range of octets that the enclosing property
          effects.
          Schema:   http://www.ietf.org/standards/dav/patch/
          Parent:   Insert, Delete, Replace
          Value:    number ["-" (number | "end")]
                    Number = 1*Digit
          Description: Octet numbering begins with 0. If the octet contains
          a single number then the operation is to begin at that octet and
          to continue for a length specified by the operation. In the case
          of a delete, this would mean to delete a single octet. In the
          case of an insert this would mean to begin the insertion at the
          specified octet and to continue for the length of the included
          value, extending the resource if necessary. In the case of
          replace, the replace begins at the specified octet and overwrites
          all that follow to the length of the included value.


          3.10.5    The Response

          200 (OK) - The request entity body was processed without error,
          resulting in an update to the state of the resource.
          409 (Conflict) - If the update information in the request message
          body does not make sense given the current state of the resource
          (e.g., an instruction to delete a non-existent line), this status
          code MAY be returned.
          415 (Unsupported Media Type) - The server does not support the
          content type of the update instructions in the request message
          body.
          416 (Unprocessable Entity) - A new status code.  The server
          understands the content type of the request entity, but was
          unable to process the contained instructions.
          417 (Insufficient Space on Resource) - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.


          3.10.6    Examples







          3.10.6.1  HTML file modification

          The following example shows a modification of the title and
          contents of the HTML resource http://www.example.org/hello.html.
          Before:
               <HTML>
               <HEAD>
               <TITLE>Hello world HTML page</TITLE>
               </HEAD>
               <BODY>
               <P>Hello, world!</P>
               </BODY>
               </HTML>
          PATCH Request:                     Response:
               PATCH hello.html HTTP/1.1
               Host: www.example.org
               Content-Type: text/xml
               Content-Length: xxx

                                             HTTP/1.1 100 Continue
               <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/patch/" AS = "D"/>
               <D:ResourceUpdate>
                    <Replace XML-SPACE = "PRESERVE"><octet-range>14</octet-
               range>&003CTITLE&003ENew Title&003C/TITLE&003E</Replace>
                    <Delete><octet-range>38-50</Delete>
               <Insert XML-SPACE = "PRESERVE"><octet-
          range>86</>&003CP&003ENew paragraph&003C/P&003E</Insert>
               </D:ResourceUpdate>
                                             HTTP/1.1 200 OK
          After:
               <HTML>
               <HEAD>
               <TITLE>New Title</TITLE>
               </HEAD>
               <BODY>
               <P>Hello, world!</P>
               <P>New paragraph</P>
               </BODY>
               </HTML>

          14
          3.11 Headers


          3.11.1    Destination Header

          The Destination header specifies a destination resource for
          methods such as COPY and MOVE, which take two URIs as parameters.
               Destination= "Destination" ":" URI


          3.11.2    Enforce-Live-Properties Header

          The Enforce-Live-Properties header specifies properties that MUST
          be "live" after they are copied (moved) to the destination
          resource of a copy (or move). If the value "*" is given for the
          header, then it designates all live properties on the source
          resource.  If the value is "Omit" then the server MUST NOT
          duplicate on the destination resource any properties that are
          defined on the source resource. If this header is not included
          then the server is expected to act as defined by the default
          property handling behavior of the associated method.
               EnforceLiveProperties = "Enforce-Live-Properties" ":" ("*" |






               "Omit" | 1#(Property-Name))
               Property-Name = "<" URI ">"


          3.11.3    Overwrite Header
          The Overwrite header specifies whether the server should
          overwrite the state of a non-null destination resource during a
          COPY or MOVE.  A value of "false" states that the server MUST NOT
          perform the COPY or MOVE operation if the state of the
          destination resource is non-null. By default, the value of
          Overwrite is "true," and a client MAY omit this header from a
          request when its value is "true." While the Overwrite header
          appears to duplicate the functionality of the If-Match: * header
          of HTTP/1.1, If-Match applies only to the Request-URI, and not to
          the Destination of a COPY or MOVE.
               Overwrite = "Overwrite" ":" ("true" | "false")
          If there is a conflict and the Overwrite header equals "true", or
          is absent and thus defaults to "true", then the method MUST fail
          with a 409 Conflict.


          3.11.4    Destroy Header15

          When deleting a resource the client often wishes to specify
          exactly what sort of delete is being enacted. The Destroy header,
          used with the Mandatory header, allows the client to specify the
          end result they desire. The Destroy header is specified as
          follows:
          The Undelete token requests that, if possible, the resource
          should be left in a state such that it can be undeleted. The
          server is not required to honor this request.
          The NoUndelete token requests that the resource MUST NOT be left
          in a state such that it can be undeleted.
          The VersionDestroy token includes the functionality of the
          NoUndelete token and extends it to include having the server
          remove all versioning references to the resource that it has
          control over.
               DestroyHeader = "Destroy" ":" #Choices
          Choices = "VersionDestroy" | "NoUndelete" | "Undelete" | token
          |"<" URI ">" ; a token extension MUST NOT be used unless it is
          specified in a RFC16, otherwise a URI MUST be used for
          extensions.


          3.11.5    Collection-Member Header

          The Collection-Member header specifies the URI of an external
          resource to be added/deleted to/from a collection.
               CollectionMember = "Collection-Member" ":" URI


          3.12 Links


          3.12.1    Source Link Property Type

          Name:     http://www.ietf.org/standards/dav/link/source
          Purpose:       The destination of the source link identifies the
          resource that contains the unprocessed source of the linkís
          source.
          Schema:        http://www.ietf.org/standards/dav/link/
          Parent:        Any
          Value:         An XML document with zero or more link XML
          elements.
          Discussion: The source of the link (src) is typically the URI of






          the output resource on which the link is defined, and there is
          typically only one destination (dst) of the link, which is the
          URI where the unprocessed source of the resource may be accessed.
          When more than one link destination exists, this specification
          asserts no policy on ordering.


          4    State Tokens

          4.1  Overview


          4.1.1     Problem Description

          There are times when a principal will want to predicate
          successful execution of a method on the current state of a
          resource.  While HTTP/1.1 provides a mechanism for conditional
          execution of methods using entity tags via the "If-Match" and
          "If-
          None-Match" headers, the mechanism is not sufficiently extensible
          to express conditional statements involving more generic state
          indicators, such as lock tokens.

          The fundamental issue with entity tags is that they can only be
          generated by a resource. However there are times when a client
          will want to be able to share state tokens between resources,
          potentially on different servers, as well as be able to generate
          certain types of lock tokens without first having to communicate
          with a server.

          For example, a principal may wish to require that resource B have
          a certain state in order for a method to successfully execute on
          resource A. If the client submits an e-tag from resource B to
          resource A, then A has no way of knowing that the e-tag is meant
          to describe resource B.

          Another example occurs when a principal wishes to predicate the
          successful completion of a method on the absence of any locks on
          a resource. It is not sufficient to submit an "If-None-Match: *"
          as this refers to the existence of an entity, not of a lock.

          This draft defines the term "state token" as an identifier for a
          state of a resource. The sections below define requirements for
          state tokens and provide a  state token syntax, along with two
          new headers which can accept the new state token syntax.


          4.1.2     Solution Requirements


          4.1.2.1   Syntax

          Self-Describing. A state token must be self describing such that
          upon inspecting a state token it is possible to determine what
          sort of state token it is, what resource(s) it applies to, and
          what state it represents.

          This self-describing nature allows servers to accept tokens from
          other servers and potentially be able to coordinate state
          information cross resource and cross site through standardized
          protocols. For example, the execution of a request on resource A
          can be predicated on the state of resource B, where A and B are
          potentially on different servers.

          Client Generable. The state token syntax must allow, when






          appropriate, for clients to generate a state token without having
          first communicated with a server.

          One drawback of entity tags is that they are set by the server,
          and there is no interoperable algorithm for calculating an entity
          tag. Consequently, a client cannot generate an entity tag from a
          particular state of a resource.  However, a state token which
          encodes an MD5 state hash could be calculated by a client based
          on a client-held state of a resource, and then submitted to a
          server in a conditional method invocation.

          Another potential use for client generable state tokens is for a
          client to generate lock tokens with wild card fields, and hence
          be able to express conditionals such as: "only execute this GET
          if there are no write locks on this resource."


          4.1.2.2   Conditonals

          Universal. A solution must be applicable to all requests.
          Positive and Negative. Conditional expressions must allow for the
          expression of both positive and negative state requirements.


          4.2  State Token Syntax
          State tokens are URLs employing the following syntax:
          State-Token = "StateToken:" Type ":" Resources ":" State-Info
          Type = "Type" "=" Caret-encoded-URL
          Resources = "Res" "=" Caret-encoded-URL
          Caret-encoded-URL = "^" Resource "^"
          Resource = <A URI where all "^" characters are escaped>
          State-Info = *(uchar | reserved)  ; uchar, reserved defined
          section 3.2.1 of RFC 2068

          This proposal has created a new URL scheme for state tokens
          because a state token names a network resource using its normal
          name, which is typically state-invariant, along with additional
          information that specifies a particular state of the resource.
          Encoding the state information into the native URL scheme of the
          network resource was not felt to be safe, since freedom from name
          space collisions could not be guaranteed. If this proposal is
          accepted, the StateToken URL scheme will need to be defined and
          registered with IANA.

          State Token URLs begin with the URL scheme name "StateToken"
          rather than the name of the particular state token type they
          represent in order to make the URL self describing. Thus it is
          possible to examine the URL and know, at a minimum, that it is a
          state token.

          Labeled name/value pairs are used within the token to allow new
          fields to be added. Processors of state tokens MUST be prepared
          to accept the fields in whatever order they are present and MUST
          ignore any fields they do not understand.
          The "Type" field specifies the type of the state information
          encoded in the state token. A URL is used in order to avoid
          namespace collisions.

          The "Res" field identifies the resource for which the state token
          specifies a particular state. Since commas and spaces are
          acceptable URL characters, a caret is used to delimit a URL.
          Since a caret is an acceptable URL character, any instances of it
          must be escaped using the % escape convention.

          The State-Info production is expanded upon in descriptions of






          specific state token types, and is intended to contain the state
          description information for a particular state token.


          4.3  State Token Conditional Headers


          4.3.1     If-State-Match

          If-State-Match = "If-State-Match" ":" ("AND" | "OR") 1#("<"
          State-
          Token ">")

          The If-State-Match header is intended to have similar
          functionality to the If-Match header defined in section 14.25 of
          RFC 2068.

          If the AND keyword is used and all of the state tokens identify
          the state of the resource, then the server MAY perform the
          requested method. If the OR keyword is used and any of the state
          tokens identifies the current state of the resource, then server
          MAY perform the requested method.  If neither of the keyword
          requirements is met, the server MUST NOT perform the requested
          method, and MUST return a 412 (Precondition Failed) response.


          4.3.2     If-None-State-Match

          If-None-State-Match = "If-None-State-Match" ":" 1#("<" State-
          Token ">")

          The If-None-State-Match header is intended to have similar
          functionality to the If-None-Match header defined in section
          14.26 of RFC 2068.

          If any of the state tokens identifies the current state of the
          resource, the server MUST NOT perform the requested method.
          Instead, if the request method was GET, HEAD, INDEX, or GETMETA,
          the server SHOULD respond with a 304 (Not Modified) response,
          including the cache-related entity-header fields (particularly
          ETag) of the current state of the resource.  For all other
          request methods, the server MUST respond with a status of 412
          (Precondition Failed).

          If none of the state tokens identifies the current state of the
          resource, the server MAY perform the requested method.

          Note that the "AND" and "OR" keywords specified with the If-
          State-
          Match header are intentionally not defined for If-None-State-
          Match, because this functionality is not required.


          4.4  State Token Header

          State-Token-Header = "State-Token" ":" 1#("<" State-Token ">")
          The State Token header is intended to have similar functionality
          to the etag header defined in section 14.20 of RFC 2068. The
          purpose of the tag is to return state tokens defined on a
          resource in a response. The contents of the state-token are not
          guaranteed to be exhaustive and are generally used to return a
          new state token that has been defined as the result of a method.
          For example, if a LOCK method were successfully executed on a
          resource the response would include a state token header with the
          lock state token included.








          4.5  E-Tags
          E-tags have already been deployed using the If-Match and If-None-
          Match headers.  Introducing two mechanisms to express e-tags
          would only confuse matters, therefore e-tags should continue to
          be expressed using quoted strings and the If-Match and If-None-
          Match headers.


          5    Locking

          5.1  Problem Description - Overview

          Locking is used to arbitrate access to a resource amongst
          principals that have equal access rights to that resource.

          This draft allows locks to vary over two parameters, the number
          of principals involved and the type of access to be granted. This
          draft will only provide for the definition of locking for one
          access type, write. However, the syntax is extensible enough to
          allow for the specification of other access types. It is a goal
          of this proposal that it use the same access verbs as will be
          defined in the access control draft.


          5.1.1     Exclusive Vs. Shared Locks

          The most basic form of LOCK is an exclusive lock. This is a lock
          where the access right in question is only granted to a single
          principal. The need for this arbitration results from a desire to
          avoid having to constantly merge results. In fact, many users so
          dislike having to merge that they would rather serialize their
          access to a resource rather than have to constantly perform
          merges.

          However, there are times when the goal of a lock is not to
          exclude others from exercising an access right but rather to
          provide a mechanism for principals to indicate that they intend
          to exercise their access right.  Shared locks are provided for
          this case. A shared lock allows multiple principals to receive a
          lock, hence any principal with appropriate access can get the
          lock.

          With shared locks there are two trust sets that affect a
          resource.  The first trust set is created by access permissions.
          Principals who are trusted, for example, may have permission to
          write the resource, those who are not, don't.  Among those who
          have access permission to write the resource, the set of
          principals who have taken out a shared lock also must trust each
          other, creating a (probably) smaller trust set within the access
          permission write set.

          Starting with every possible principal on the Internet, in most
          situations the vast majority of these principals will not have
          write access to a given resource.  Of the small number who do
          have write access, some principals may decide to guarantee their
          edits are free from overwrite conflicts by using exclusive write
          locks in conjunction with a precondition header (If-State-Match)
          that checks for existence of the lock prior to writing the
          resource. Others may decide they trust their collaborators (the
          potential set of collaborators being the set of principals who
          have write permission) and use a shared lock, which informs their
          collaborators that a principal is potentially working on the
          resource.







          The WebDAV extensions to HTTP do not need to provide all of the
          communications paths necessary for principals to coordinate their
          activities.  When using shared locks, principals may use any out
          of band communication channel to coordinate their work (e.g.,
          face-to-face interaction, written notes, post-it notes on the
          screen, telephone conversation, email).  The intent of a shared
          lock is to let collaborators know who else is potentially working
          on a resource.

          Why not use exclusive write locks all the time?  Experience from
          initial Web distributed authoring systems has indicated that
          exclusive write locks are often too rigid.  An exclusive write
          lock is used to enforce a particular editing process: take out
          exclusive write lock, read the resource, perform edits, write the
          resource, release the lock.  What happens if the lock isn't
          released?  While the time-out mechanism provides one solution, if
          you need to force the release of a lock immediately, it doesn't
          help much.  Granted, an administrator can release the lock for
          you, but this could become a significant burden for large sites.
          Further, what if the administrator can't be reached immediately?

          Despite their potential problems, exclusive write locks are
          extremely useful, since often a guarantee of freedom from
          overwrite conflicts is exactly what is needed.  The solution:
          provide exclusive write locks, but also provide a less strict
          mechanism in the form of shared locks which can be used by a set
          of people who trust each other and who have access to a
          communications channel external to HTTP which can be used to
          negotiate writing to the resource.


          5.1.2     Required Support

          A DAV compliant server is not required to support locking in any
          form. If the server does support locking it may choose to support
          any combination of exclusive and shared locks for any access
          types.

          The reason for this flexibility is that server implementers have
          said that they are willing to accept minimum requirements on all
          services but locking. Locking policy strikes to the very heart of
          their resource management and versioning systems and they require
          control over what sort of locking will be made available. For
          example, some systems only support shared write locks while
          others only provide support for exclusive write locks. As each
          system is sufficiently different to merit exclusion of certain
          locking features, the authors are proposing that locking be
          allowed as the sole axis of negotiation within DAV.


          5.2  LOCK Method


          5.2.1     Operation

          A lock method invocation creates the lock specified by the Lock-
          Info header on the request-URI. Lock method requests SHOULD NOT
          have a request body. A user-agent SHOULD submit an Owner header
          field with a lock request.

          A successful response to a lock invocation MUST include a Lock-
          Token header. If the server supports a time based lock removal
          mechanism on the resource, a successful lock invocation SHOULD
          return a Time-Out header.








          5.2.2     Effect of Locks on Properties and Containers

          By default a lock affects the entire state of the resource,
          including its associated properties. As such it is illegal to
          specify a lock on a property. For containers, a lock also affects
          the ability to add or remove members. The nature of the effect
          depends upon the type of access control involved.  The Depth
          header expresses the general semantics of a LOCK method request
          when invoked on a collection (note that specific lock types may
          restrict the effect of a lock, for example limiting the allowable
          values of the Depth header):
          ∑    A Depth header (defined in the namespace draft) may be used
            on a LOCK method when the LOCK method is applied to a
          collection
            resource. The legal values for Depth on a LOCK are 0, 1, and
            Infinity. A Depth of 0 instructs the resource to just lock the
            container. As previously mentioned, depending on the type of
            lock, the lock affects the ability to add or remove members of
            the container.
          ∑    A Depth of 1 means that the container is locked and a LOCK
            is executed on the containerís propagate members with a Depth
          of
            0 and If-Range, If-Modified-Since, If-Unmodified-Since, If-
          Match
            and If-None-Match headers are dropped. However, the effects of
            the LOCK MUST be atomic in that either the container and all of
            its members are locked or no lock is granted. The result of a
            Depth 1 lock is a single lock token which represents the lock
          on
            the container and all of its members. This lock token may be
          used
            in an If-State-Match or If-Not-State-Match header against any
          of
            the resources covered by the lock. Since the lock token
            represents a lock on all the resources, an UNLOCK using that
            token will remove the lock from all included resources, not
          just
            the resource the UNLOCK was executed on.
          ∑    A Depth of infinity means that the LOCK is recursively
            executed, with a Depth of infinity, on the collection and all
          of
            its propagate members and all of their propagate members. As
          with
            a Depth of 1, the LOCK must be granted in total or not at all.
            Otherwise the lock operates in the same manner as a Depth of 1
            lock.

          The default behavior when locking a container is to act as if a
          "Depth: 0" header had been placed on the method.


          5.2.3     Locking Replicated Resources

          Some servers automatically replicate resources across multiple
          URLs. In such a circumstance the server MAY only accept a lock on
          one of the URLs if the server can guarantee that the lock will be
          honored across all the URLs.


          5.2.4     Interaction with other Methods

          Only two methods, MOVE and DELETE, have side effects which
          involve locks. When a resource is moved, its lock SHOULD be moved






          with it. However this may not always be possible and there is
          currently no proposal to create a header which would specify that
          the lock request should fail if the resourceís locks can not be
          maintained. A COPY MUST NOT copy any locks on the source resource
          over to the destination resource. Deleting a resource MUST remove
          all locks on the resource.


          5.2.5     Lock Compatibility Table

          The table below describes the behavior that occurs when a lock
          request is made on a resource.

          Current lock state/      Shared Lock       Exclusive Lock
          Lock request
          None                     True              True
          Shared Lock              True              False
          Exclusive Lock           False             False*

          Legend: True = lock MAY be granted.  False = lock MUST NOT be
          granted.  *=if the principal requesting the lock is the owner of
          the lock, the lock MAY be regranted.

          The current lock state of a resource is given in the leftmost
          column, and lock requests are listed in the first row.  The
          intersection of a row and column gives the result of a lock
          request.  For example, if a shared lock is held on a resource,
          and an exclusive lock is requested, the table entry is "false",
          indicating the lock must not be granted.

          If an exclusive lock is re-requested by the principal who owns
          the lock, the lock MAY be regranted. If the lock is regranted,
          the same lock token that was previously issued MUST be returned.


          5.2.6     Status Codes

          412 "Precondition Failed" - The included state-token was not
          enforceable on this resource.

          416 "Locked" - The resource is locked so the method has been
          rejected.


          5.2.7     Example

          LOCK /workspace/webdav/proposal.doc HTTP/1.1
          Host: webdav.sb.aol.com
          Lock-Info: LockType=Write LockScope=Exclusive
          Owner: <http://www.ics.uci.edu/~ejw/contact.html>


          HTTP/1.1 200 OK
          State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.
          ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockSco
          pe=Exclusive:ServerID=12382349AdfFFF
          Time-Out: ClockType=Activity TimeType=second;604800
          This example shows the successful creation of an exclusive write
          lock on resource
          http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The
          resource http://www.ics.uci.edu/~ejw/contact.html contains
          contact information for the owner of the lock. The server has an
          activity-based timeout policy in place on this resource, which
          causes the lock to automatically be removed after 1 week (604800
          seconds). The response has a Lock-Token header that gives the






          state token URL for the lock token generated by this lock
          request.


          5.2.8     Lock-Info Request Header

          The Lock-Info header specifies the scope and type of a lock for a
          LOCK method request. The syntax specification below is
          extensible, allowing new type and scope identifiers to be added.
          LockInfo = "Lock-Info" ":" DAVLockType SP DAVLockScope CRLF
          DAVLockType = "LockType" "=" DAVLockTypeValue
          DAVLockTypeValue = ("Write" | *(uchar | reserved))
          DAVLockScope = "LockScope" "=" DAVLockScopeValue
          DAVLockScopeValue = ("Exclusive" |"Shared" | *(uchar | reserved))


          5.2.9     Owner Request Header


          5.2.9.1   Problem Description

          When discovering the list of owners of locks on a resource, a
          principal may want to be able to contact the owner directly. For
          this to be possible the lock discovery mechanism must provide
          enough information for the lock owner to be contacted.


          5.2.9.2   Solution Requirements

          Not all systems have authentication procedures that provide
          sufficient information to identify a particular user in a way
          that is meaningful to a human. In addition, many systems that do
          have sufficient information, such as a name and e-mail address,
          do not have the ability to associate this information with the
          lock discovery mechanism. Therefore a means is needed to allow
          principals to provide authentication in a manner which will be
          meaningful to a human.

          The From header (defined in RFC 2068), which contains only an
          email mailbox, is not sufficient for the purposes of quick
          identification. When desperately looking for someone to remove a
          lock, e-mail is often not sufficient. A telephone number (cell
          number, pager number, etc.) would be better. Furthermore, the
          email address in the From field may or may not support including
          the owners name and that name is often set to an alias anyway.
          Therefore a header more flexible than From is required.


          5.2.9.3   Syntax

          Owner = "Owner" ":" (("<" URI ">")  | quoted-string)
          The URI SHOULD provide a means for either directly contacting the
          principal (such as a telephone number or e-mail URI), or for
          discovering the principal (such as  the URL of a homepage).  The
          quoted string SHOULD provide a means for directly contacting the
          principal, such as a name and telephone number.


          5.2.10    Time-Out Header


          5.2.10.1  Problem Description

          In a perfect world principals take out locks, use the resource as
          needed, and then remove the lock when it is no longer needed.






          However, this scenario is frequently not completed, leaving
          active but unused locks. Reasons for this include client programs
          crashing and loosing information about locks, users leaving their
          systems for the day and forgetting to remove their locks, etc. As
          a result of this behavior, servers need to establish a policy by
          which they can remove a lock without input from the lock owner.
          Once such a policy is instituted, the server also needs a
          mechanism to inform the principal of the policy.


          5.2.10.2  Solution Requirements

          There are two basic lock removal policies, administrator and time
          based remove. In the first case a principal other than the lock
          owner has sufficient access rights to order the lock removed,
          even though they did not take it out. User-agents MUST assume
          that such a mechanism is available and thus locks may arbitrarily
          disappear at any time. If their actions require confirmation of
          the existence of a lock then the If-State headers are available.

          The second solution, is the time based removal policy. Activity
          based systems set a timer as soon as the lock is taken out. Every
          time a method is executed on the resource, the timer is reset. If
          the timer runs out, the lock is removed.

          Finally, some systems only allow locks to exist for the duration
          of a session, where a session is defined as the time when the
          HTTP connection that was used to take out the lock remains
          connected. This mechanism is used to allow programs which are
          likely to be improperly exited, such as JAVA programs running in
          a browser, to take out locks without leaving a lot of ownerless
          locks around when they are improperly exited.


          5.2.10.3  Syntax

          TimeOut = "Time-Out" ":" ((TimeOutType SP Session) | TimeOutVal |
                    Session) CRLF
          TimeOutType = ClockType SP TimeType
          ClockType = "ClockType" "=" ClockTypeValue
          ClockTypeValue = "Activity"
          TimeType = "TimeType" "=" TimeTypeValue
          TimeTypeValue = "Second" ";" DAVTimeOutVal
          DAVTimeOutVal = 1*digit
          Session = "Session" "=" ("Yes" | "No")

          The "Second" TimeType specifies the number of seconds that may
          elapse before the lock is automatically removed. A server MUST
          not generate a time out value for "second" greater than 2^32-1.

          If no time based system is in use then a Time-Out header MUST NOT
          be returned. The Time-Out header MUST only be returned in a
          response to a LOCK request.When session is set to yes then
          whatever clocktype and timetype is being used, their effects are
          scoped within that particular session. So an absolute lock with a
          ten day expiration period will only remain active so long as the
          session remains active. A DAVTimeOutVal value must be greater
          than zero.

          Clients MAY include TimeOut headers in their LOCK requests.
          However the server is not required to honor or even consider the
          request. The primary purpose in allowing clients to submit a
          TimeOut header is to inform the server if the client is
          requesting a session based lock. If a timeout is associated with
          the lock, the server MUST return a TimeOut header with a valid






          value.


          5.2.11    State-Token Header


          5.2.11.1  Problem Definition

          Program A, used by User A, takes out a write lock on a resource.
          Program B, also run by User A, then proceeds to perform a PUT to
          the locked resource. The PUT will succeed because locks are
          associated with a principal, not a program, and thus program B,
          because it is acting with principal Aís credential, will be
          allowed to perform the PUT. In reality program B had no knowledge
          of the lock and had it had such knowledge, would not have
          overwritten the resource. Hence, a mechanism is needed to prevent
          different programs from accidentally ignoring locks taken out by
          other programs with the same authorization.


          5.2.11.2  Solution Requirement

          The solution must not require principals to perform discovery in
          order to prevent accidental overwrites as this could cause race
          conditions.

          The solution must not require that clients guess what sorts of
          locks might be used and use if-state-match headers with wildcards
          to prevent collisions. The problem with trying to "guess" which
          locks are being used is that new lock types might be introduced,
          and the program would not know to "guess them". So, for example,
          a client might put in an if-state-match header with a wildcard
          specifying that if any write lock is outstanding then the
          operation should fail. However a new read/write lock could be
          introduced which the client would not know to put in the header.


          5.2.11.3  State-Token Header

          The State-Token header is returned in a successful response to
          the LOCK method or is used as a request header with the UNLOCK
          method.

          The State-Token header containing a lock token owned by the
          request principal is used by the principal on arbitrary method to
          indicate that the principal is aware of the specified lock. If
          the State-Token header with the appropriate lock token is not
          included the request MUST be rejected, even though the requesting
          principal has authorization to make modifications specified by
          the lock type. This injunction does not apply to methods that are
          not affected by the principalís lock.

          For example, Program A, used by user A, takes out a write lock on
          a resource. Program A then makes a number of PUT requests on the
          locked resource, all the requests contain a State-Token header
          which includes the write lock state token. Program B, also run by
          User A, then proceeds to perform a PUT to the locked resource.
          However program B was not aware of the existence of the lock and
          so does not include the appropriate state-token header. The
          method is rejected even though principal A is authorized to
          perform the PUT. Program B can, if it so chooses, now perform
          lock discovery and obtain the lock token. Note that program A and
          B can perform GETs without using the state-token header because
          the ability to perform a GET is not affected by a write lock.






          Note that having a lock state token provides no special access
          rights. Anyone can find out anyone elseís lock state token by
          performing lock discovery. Locks are to be enforced based upon
          whatever authentication mechanism is used by the server, not
          based on the secrecy of the token values.

          5.3  Write Lock

          A write lock prevents a principal without the lock from
          successfully executing a PUT, POST, DELETE, MKCOL, PROPPATCH,
          PATCH, ADDREF or DELREF on the locked resource. All other
          methods, GET in particular, function independent of the lock.

          While those without a write lock may not alter a property on a
          resource it is still possible for the values of live properties
          to change, even while locked, due to the requirements of their
          schemas. Only dead properties and live properties defined to
          respect locks are guaranteed to not change while locked.

          It is possible to assert a write lock on a null resource in order
          to lock the name. Please note, however, that locking a null
          resource effectively makes the resource non-null as the resource
          now has lock related properties defined on it.

          Write locking a container also prevents adding or removing
          members of the container. This means that attempts to PUT/POST a
          resource into the immediate name space of the write locked
          container MUST fail if the principal requesting the action does
          not have the write lock on the container. In order to keep the
          behavior of locking containers consistent all locks on containers
          MUST contain a Depth header equal to infinity, any other value is
          illegal.


          5.4  Lock Tokens


          5.4.1     Problem Description

          It is possible that once a lock has been granted it may be
          removed without the lock ownerís knowledge. This can cause
          serialization problems if the lock owner executes methods
          thinking their lock is still in effect. Thus a mechanism is
          needed for a principal to predicate the successful execution of a
          message upon the continuing existence of a lock.


          5.4.2     Proposed Solution

          The proposed solution is to provide a lock token in the response
          of a lock request. The lock token is a type of state token and
          describes a particular lock. The same lock token must never be
          repeated on a particular resource. This prevents problems with
          long held outstanding lock tokens being confused with newer
          tokens. This uniqueness requirement is the same as for e-tags.
          This requirement also allows for tokens to be submitted across
          resources and servers without fear of confusion.


          5.4.3     Lock Token Definition

          The lock token is returned in the State-Token header in the
          response to a LOCK method. The lock token can also be discovered
          through lock discovery on a resource.
          Lock-Token-URL = "StateToken:" Type ":" Resources ":" State-Info






          Type = "Type" "=" "^DAV:/LOCK/DAVLOCK^"
          Resources = "Res" "=" 1*("^" Caret-Encoded-URI "^")
          Caret-Encoded-URI = <This is a URI which has all "^"s % encoded.>
          State-Info = DAVLockScope ":" DAVLockType ":" ServerID  ;
          DAVLockScope, DAVLockType defined in Lock-Info header
          ServerID = "ServerID" "=" *(uchar | reserved)

          The ServerID is a field for use by the server. Its most basic
          purpose is to put in a unique identifier to guarantee that a
          server will never confuse an old lock token with a newer one.
          However the server is free to use the field to record whatever
          information it deems fit. The field is opaque to clients.


          5.5  UNLOCK Method


          5.5.1     Problem Definition

          The UNLOCK method removes the lock identified by the lock token
          in the State-Token header from the Request-URI.


          5.5.2     Example

          UNLOCK /workspace/webdav/proposal.doc HTTP/1.1
          Host: webdav.sb.aol.com
          State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.
          ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockSco
          pe=Exclusive:ServerID=12382349AdfFFF


          HTTP/1.1 200 OK

          In this example, the lock from example of Section 2.9 is removed
          from the resource at
          http://webdav.sb.aol.com/workspace/webdav/proposal.doc


          5.6  Discovery Mechanisms


          5.6.1     Lock Type Discovery


          5.6.1.1   Problem Definition

          Since server lock support is optional, a client trying to lock a
          resource on a server can either try the lock and hope for the
          best or can perform some form of discovery to determine what lock
          types the server actually supports, then formulate a supported
          request.  This is known as lock type discovery. Lock type
          discovery is not the same as discovering what access control
          types are supported, as there may be access control types without
          corresponding lock types.


          5.6.1.2   SupportedLock Property

          Name: http://www.ietf.org/standards/dav/lock/supportedlock
          Purpose: To provide a listing of the lock types supported by the
          resource.
          Schema: http://www.ietf.org/standards/dav/
          Values: An XML document containing zero or more LockEntry XML
          elements.






          Description: The SupportedLock property of a resource returns a
          listing of the combinations of scope and access types which may
          be specified in a lock request on the resource. Note that the
          actual contents are themselves controlled by access controls so a
          server is not required to provide information the client is not
          authorized to see. If SupportedLock is available on "*" then it
          MUST define the set of locks allowed on all resources on that
          server.


          5.6.1.3   LOCKENTRY XML Element

          Name: http://www.ietf.org/standards/dav/lockentry
          Purpose: Defines a DAVLockType/LockScope pair which may be
          legally used with a LOCK on the specified resource.
          Schema: HYPERLINK http://www.ietf.org/standards/dav/
          Parent: A SupportedLock entry
          Values: LockType LockScope


          5.6.1.4   LOCKTYPE XML Element

          Name: http://www.ietf.org/standards/dav/locktype
          Purpose: Lists a DAVLockType
          Schema: http://www.ietf.org/standards/dav/
          Parent: LOCKENTRY
          Values: DAVLockTypeValue


          5.6.1.5   LOCKSCOPE XML Element

          Name: http://www.ietf.org/standards/dav/lockscope
          Purpose: Lists a DAVLockScope
          Schema: http://www.ietf.org/standards/dav/
          Parent: LOCKENTRY
          Values: DAVLockScopeValue


          5.6.2     Active Lock Discovery


          5.6.2.1   Problem Definition

          If another principal locks a resource that a principal wishes to
          access, it is useful for the second principal to be able to find
          out who the first principal is.


          5.6.2.2   Solution Requirements

          The lock discovery mechanism should provide a list of who has the
          resource locked, what locks they have, and what their lock tokens
          are. The lock tokens are useful in shared lock situations where
          two principals in particular may want to guarantee that they do
          not overwrite each other. The lock tokens are also useful for
          administrative purposes so that an administrator can remove a
          lock by referring to its token.


          5.6.2.3   LOCKDISCOVERY Property

          Name: http://www.ietf.org/standards/dav/lockdiscovery
          Purpose: To discover what locks are active on a resource
          Schema: http://www.ietf.org/standards/dav/
          Values= An XML document containing zero or more ActiveLock XML






          elements.
          Description: The LOCKDISCOVERY property returns a listing of who
          has a lock, what type of lock they have, the time out type and
          the time remaining on the time out, and the associated lock
          token. The server is free to withhold any or all of this
          information if the requesting principal does not have sufficient
          access rights to see the requested data.


          5.6.2.4   ACTIVELOCK XML Element

          Name: http://www.ietf.org/standards/dav/activelock
          Purpose: A multivalued XML element that describes a particular
          active lock on a resource
          Schema: http://www.ietf.org/standards/dav/
          Parent: A LOCKDISCOVERY entry
          Values= LOCKTYPE LOCKSCOPE OWNER TIMEOUT LOCKTOKEN


          5.6.2.5   OWNER XML Element

          Name: http://www.ietf.org/standards/dav/lock/owner
          Purpose: Returns owner information
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= XML:REF | {any valid XML string}


          5.6.2.6   TIMEOUT XML Element

          Name: http://www.ietf.org/standards/dav/timeout
          Purpose: Returns information about the timeout associated with
          the lock
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= CLOCKTYPE TIMETYPE TIMEOUTVAL


          5.6.2.7   CLOCKTYPE XML Element

          Name: http://www.ietf.org/standards/dav/clocktype
          Purpose: Returns the clock type used with this lock
          Schema: http://www.ietf.org/standards/dav/
          Parent: TIMEOUT
          Values=  ClockTypeValue


          5.6.2.8   TIMETYPE XML Element

          Name: http://www.ietf.org/standards/dav/clocktype
          Purpose: Returns the time type used with this lock
          Schema: http://www.ietf.org/standards/dav/
          Parent: TIMEOUT
          Values= TimeTypeValue


          5.6.2.9   TIMEOUTVAL XML Element

          Name: http://www.ietf.org/standards/dav/timeoutval
          Purpose: Returns the amount of time left on the lock
          Schema: http://www.ietf.org/standards/dav/
          Parent: TIMEOUT
          Values= DAVTimeOutVal






          5.6.2.10  LOCKTOKEN XML Element
          Name: http://www.ietf.org/standards/dav/statetoken
          Purpose: Returns the lock token
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= XML:REF
          Description: The REF contains a Lock-Token-URL.


          6    Version Control
          [TBD]


          7    Internationalization Support
          [TBD]


          8    Security Considerations
          [TBD]


          9    Acknowledgements

          Terry Allen, Harald Alvestrand, Alan Babich, Dylan Barrell,
          Bernard Chester, Dan Connolly, Jim Cunningham, Ron Daniel, Jr.,
          Keith Dawson, Mark Day, Martin Duerst, David Durand, Lee Farrell,
          Chuck Fay, Roy Fielding, Mark Fisher, Alan Freier, George
          Florentine, Jim Gettys, Phill Hallam-Baker, Dennis Hamilton,
          Steve Henning, Alex Hopmann, Andre van der Hoek, Ben Laurie, Paul
          Leach, Ora Lassila, Karen MacArthur, Steven Martin, Larry
          Masinter, Michael Mealling, Keith Moore, Henrik Nielsen, Kenji
          Ota, Bob Parker, Glenn Peterson, Jon Radoff, Saveen Reddy, Henry
          Sanders, Christopher Seiwald, Judith Slein, Mike Spreitzer, Einar
          Stefferud, Ralph Swick, Kenji Takahashi, Robert Thau, Sankar
          Virdhagriswaran, Fabio Vitali, Gregory Woodhouse, Lauren Wood


          10   References

          [Berners-Lee, 1997] T. Berners-Lee, "Metadata Architecture."
          Unpublished white paper, January 1997.
          http://www.w3.org/pub/WWW/DesignIssues/Metadata.html.

          [Bray, Sperberg-McQueen, 1997] T. Bray, C. M. Sperberg-McQueen,
          "Extensible Markup Language (XML): Part I. Syntax", WD-xml-
          lang.html, http://www.w3.org/pub/WWW/TR/WD-xml-lang.html.

          [Connolly et al, 1997] D. Connolly, R. Khare, H.F. Nielsen, "PEP
          - an Extension Mechanism for HTTP", Internet draft, work-in-
          progress. draft-ietf-http-pep-04.txt,
          ftp://ds.internic.net/internet-drafts/draft-ietf-http-pep-04.txt.

          [Fielding et al., 1997] R. Fielding, J. Gettys, J. Mogul, H.
          Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol --
          HTTP/1.1." RFC 2068. U.C. Irvine, DEC, MIT/LCS.  January, 1997.

          [Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for
          Bibliographic Records," RFC 1807. Stanford, Myricom. June, 1995.

          [Maloney, 1996] M. Maloney, "Hypertext Links in HTML." Internet
          draft (expired), work-in-progress, January, 1996.

          [MARC, 1994] Network Development and MARC Standards, Office, ed.
          1994. "USMARC Format for Bibliographic Data", 1994. Washington,
          DC: Cataloging Distribution Service, Library of Congress.







          [Miller et al., 1996] J. Miller, T. Krauskopf, P. Resnick, W.
          Treese, "PICS Label Distribution Label Syntax and Communication
          Protocols" Version 1.1, W3C Recommendation REC-PICS-labels-
          961031. http://www.w3.org/pub/WWW/TR/REC-PICS-labels-961031.html.

          [Slein et al., 1997] J. A. Slein, F. Vitali, E. J. Whitehead,
          Jr., D. Durand, "Requirements for Distributed Authoring and
          Versioning on the World Wide Web." Internet-draft, work-in-
          progress, draft-ietf-webdav-requirements-02.txt,
          ftp://ds.internic.net/internet-drafts/draft-ietf-webdav-
          requirements-02.txt.

          [WebDAV, 1997] WEBDAV Design Team. "A Proposal for Web Metadata
          Operations." Unpublished manuscript.
          http://www.ics.uci.edu/~ejw/authoring/proposals/metadata.html

          [Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R. Daniel,
          "OCLC/NCSA Metadata Workshop Report."
          http://purl.oclc.org/metadata/dublin_core_report.

          [Yergeau, 1997] F. Yergeau, "UTF-8, a transformation format of
          Unicode and ISO 10646", Internet Draft, work-in-progress, draft-
          yergeau-utf8-rev-00.txt, http://www.internic.net/internet-
          drafts/draft-yergeau-utf8-rev-00.txt.


          11   Authors' Addresses

          Y. Y. Goland
          Microsoft Corporation
          One Microsoft Way
          Redmond, WA 98052-6399
          Email yarong@microsoft.com

          E. J. Whitehead, Jr.
          Dept. Of Information and Computer Science
          University of California, Irvine
          Irvine, CA 92697-3425
          Email: ejw@ics.uci.edu

          A. Faizi
          Netscape
          685 East Middlefield Road
          Mountain View, CA 94043
          Email: asad@netscape.com

          S. R Carter
          Novell
          1555 N. Technology Way
          M/S ORM F111
          Orem, UT 84097-2399
          Email srcarter@novell.com

          D. Jensen
          Novell
          1555 N. Technology Way
          M/S ORM F111
          Orem, UT 84097-2399
          Email dcjensen@novell.com