WEBDAV Working Group E. Christian INTERNET DRAFT U.S. Geological Survey Expires October, 2000 April 24, 2000 Use of a Semantics Register with WebDAV Properties 1. Status of this Document This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. Abstract This document specifies a mechanism to associate a WebDAV ([WEBDAV]) property with an entry in a Semantics Register. A Semantics Register documents the meaning of properties in a formal manner and may be implemented with schema technologies such as Extensible Markup Language (XML) Schema ([XMLSCHEMA]) or Resource Description Framework (RDF) Schema ([RDFS]). Schema technologies expose the derivation of complex properties from simpler concepts, as demonstrated in the Basic Semantics Register ([BSR]) for data elements used in Electronic Data Interchange. Registering the meanings of properties in this manner can enhance interoperability across systems and throughout the long-term information life cycle. 3. Introduction The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [MUSTS] . This document specifies how a WebDAV ([WEBDAV]) property can be associated with an entry in a Semantics Register. The Semantics Register may be implemented with schema technologies such as XML Schema ([XMLSCHEMA]), Resource Description Framework RDF) Schema, and perhaps others that use the XML Namespaces [XMLNS] mechanism. Christian INTERNET-DRAFT [Page 1] INTERNET-DRAFT Semantics Register with WebDAV April 24, 2000 WebDAV defines a protocol for manipulating the contents of properties in a Web object instance. Each such property is referenced in WebDAV by a name that is unique within a specific namespace. It is often important to associate with a property some assertions in addition to its name and contents: assertions such as alternate labels or the property's semantic or syntactic relationship to other properties in the same or other systems. In organizing these assertions, a Semantics Register serves as an important tool for documenting a system and enabling interoperability among systems. When implemented with schema technologies, a Semantics Register can expose how complex properties are derived from simpler concepts. This use is demonstrated in the Basic Semantics Register ([BSR]), wherein thousands of complex data elements used in Electronic Data Interchange are constructed from commonly understood concepts. 4. Semantics Register referenced through a WebDAV Namespace A Semantics Register can be referenced within WebDAV through the XML Namespace ([XMLNS]) attribute. For example, assume there is a Semantics Register for Open Document Management ([ODMA]) properties at the URI "http://www.semantics.org/reg/odm.rdfs", and one of the ODM properties has an attribute ID "ODM_CHECKEDOUTBY". This hypothetical Semantics Register can be referenced in the value of an "xmlns" attribute on the "prop" element of a WebDAV "propfind", e.g., 5. Example Semantics Register On the Web, a simple Semantics Register can be implemented using XML Schema ([XMLSCHEMA])or RDF Schema ([RDFS]). For semantic concepts and data elements, XML Schema employs "Types" and "Elements" where RDF Schema employs "Classes" and "Properties". Relationships among these can be defined in either schema technology, so that complex entities can be formally defined as comprised of simpler entities. In the RDF Schema technology, every Class or Property is defined by an "RDF Description". A particular WebDAV property can be associated with a particular RDF Description by matching the WebDAV property name with the ID attribute of the RDF Description. From the example above, the WebDAV property name "odm:ODM_CHECKEDOUTBY" may correspond to this RDF Description entry in the hypothetical Semantics Register: Christian INTERNET-DRAFT [Page 2] INTERNET-DRAFT Semantics Register with WebDAV April 24, 2000 Username of the person who has the document checked-out. Each RDF Description in a schema referenced by a WebDAV namespace can contain various assertions about the WebDAV property. These assertions are expressed as RDF Schema elements and attributes. Assertions about the WebDAV property include label, subClassOf, subPropertyOf, domain, range, comment, and isDefinedBy, among others. Here, for example, is a fuller entry for the ODM_CHECKEDOUTBY property as it might exist in the hypothetical Semantics Register: Username of the person who has the document checked-out. 6. Internationalization Considerations The international considerations of the mechanism to associate a WebDAV property with an entry in a Semantics Register are affected by both WebDAV and the specific Semantics Register technology used. WebDAV uses XML ([XML]) and inherits the relatively robust support in XML for internationalization. The only Semantics Register technology discussed here is the RDF Schema specification, which also uses XML. 7. Security Considerations The mechanism to associate WebDAV properties with a Semantics Register does not itself affect security. Any security considerations are a function of WebDAV technology and the specific Semantics Register technology. When implemented using Internet protocols and data representation techniques, both technologies inherit the security characteristics of those protocols and techniques. 8. IANA Considerations The mechanism to associate WebDAV properties with a Semantics Register does not itself introduce any new IANA considerations. It makes use of namespaces as they may be defined for WebDAV and for any particular Semantics Registry technology such as RDF Schema. Christian INTERNET-DRAFT [Page 3] INTERNET-DRAFT Semantics Register with WebDAV April 24, 2000 9. Copyright and Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. 11. Acknowledgements Many groups and individuals contributed to the various technologies and ideas that form the substance of this Internet-Draft. The author especially acknowledges the contributions of Jim Whitehead in the WebDAV area, Eric Miller in the area of RDF, Andrew Layman in XML Namespaces, Bruce Bargmeyer in Semantics Registers, Denis Hill in the Basic Semantics Register, and Owen Ambur in the area of Open Document Management Attributes. 12. References [BSR] Basic Semantics Register demo (This site is for demonstration of technology only. The BSR content is under review in ISO). . [MUSTS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119, Harvard University, March 1997. [ODMA] Open Document Management API (ODMA) version 2.0, May 1998, Association for Information and Image Management. . [RDFS] Resource Description Framework (RDF) Schema Specification, March 1999, World Wide Web Consortium Proposed Recommendation PR-rdf-schema-19990303. [WEBDAV] Y. Y. Goland, E. J. Whitehead, Jr., A. Faizi, S. R. Carter, D. Jensen, "Extensions for Distributed Authoring on the World Wide Web - WebDAV." RFC 2518. Microsoft, U.C. Irvine, Netscape, Novell. April, 1998. Christian INTERNET-DRAFT [Page 4] INTERNET-DRAFT Semantics Register with WebDAV April 24, 2000 [XML] Extensible Markup Language (XML) 1.0, February 1998, World Wide Web Consortium Recommendation Rec-xml-19980210. . [XMLNS] Namespaces in XML, January 1999, World Wide Web Consortium Recommendation REC-xml-names-19990114. . [XMLSCHEMA] XML Schema Part 1 - Strctures, April, 2000, World Wide Web Consortium Working Draft. 13. Expiration This Internet-Draft expires October 24, 2000. 14. Discussion mailing list Comments may be sent to the WebDAV mailing list, w3c-dist-auth@w3.org. 15. Author's Address Eliot Christian U.S. Geological Survey 802 National Center Reston, VA 20192 echristi@usgs.gov Christian [Page 5]