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Created: March 17, 2006.
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WS-Transfer, WS-Eventing, and WS-Enumeration Specifications Submitted to W3C.

Contents

On March 15, 2006, W3C acknowledged receipt of three Member Submissions from leading industry partners including BEA Systems, Computer Associates, IBM, Intel, Microsoft, Sonic Software, Systinet, and TIBCO Software for WS-* specifications relating to resources, events, and management. Also on March 15, 2006 a Joint White Paper Toward Converging Web Service Standards for Resources, Events, and Management was published by Hewlett Packard Corporation, IBM Corporation, Intel Corporation, and Microsoft Corporation.

The Joint White Paper outlines a plan to "develop a common set of specifications for resources, events, and management that can be broadly supported across multiple platforms." The common functionality covered by these specifications is intended to include: (1) "Resources: the ability to create, read, update and delete information using Web services; (2) Events: the ability to connect Web services together using an event driven architecture based on publish and subscribe; (3) Management: providing a Web service model for building system and application management solutions, focusing on resource management."

For information management, two new WS-* specifications (WS-Transfer Addendum, WS-ResourceTransfer) and a new version of an existing specification (WS-MetadataExchange) will be produced by HP, IBM, Intel, and Microsoft. "These specifications layer on and compose with WS-Transfer and WS-Enumeration, which HP, IBM, Intel and Microsoft will support."

WS-Transfer Addendum extends the September 2004 version of WS-Transfer by "defining optional 'Get', Put', and 'Create' messages, allowing the message body element to specify a subset of the resource or to convey resource-specific processing directives. The dialect of the body element is resource specific and is defined by specifications layered on WS-Transfer Addendum. WS-Transfer Addendum also extends the 'Put' and 'Create' responses so they may include the WS-Addressing endpoint reference (EPR) for the updated/new resource."

The new WS-ResourceTransfer specification will define new message body elements that support creating, retrieving, and updating partial elements of a resource. Among the motivations for supporting access to sub-elements of a resource's state: improved performance (a resource's state may be very large, while the requestor only needs sub-elements) and allowing partial updates, which eliminates unnecessary side effects due to updating entire documents. For example, updating an entire Directory entry could reset a password lifetime timer whereas simply updating the email address would not. Additionally, WS-RT defines an optional resource lifetime, a lifetime metadata format and associated WS-MetadataExchange dialect, semantics for processing lifetime metadata when included in a 'Create' request, and how a resource EPR may include the mex:Metadata element."

The W3C Team Comment on WS-Transfer itself observes that WS-Transfer is a "SOAP-based protocol for manipulating resources and their representations. One can create, modify, delete resources, as well as retrieve representations of those resources... There is an obvious parallel between WS-Transfer and the Hypertext Transfer Protocol (HTTP/1.1) and the Web itself, including (1) the concept of resources which are manipulated via representations, similar to Web resources, and (2) the operations on resources are similar, with the WS-Addressing [action] property corresponding to the HTTP method" (GET, PUT, DELETE, CREATE).

For eventing and notification, HP, IBM, Intel, and Microsoft are defining a new WS-EventNotification specification that integrates functions from WS-Notification with WS-Eventing. The new specification layers on and composes with WS-Eventing; WS-EventNotification introduces five capabilities that WS-Notification already supports.

For subscription policy, WS-EventNotification "defines concrete policies that allow a resource/service to describe its approaches for subscriptions and subscription management, and allows a subscriber to specify directives to the event source. WS-EventNotification introduces richer filter languages, building upon facilities introduced in WS-Eventing. WS-EventNotification also introduces 'wrapped notification' to support systems that require an explicit notification message that contains the event data. In wrapped notification, the output message/operation for the event is contained within an outer notify operation/message; wrapped notification also provides a generic interface for receiving notifications. WS-EventNotification will support subscription resources in terms of a lifetime: the subscriber can use 'Get', Put', and 'Delete' to read or update the subscription's state, for example to change a filter or expiration lifetime. Finally, WS-EventNotification introduces the notion of pausing a subscription, which allows for the temporary halting the flow of Notifications to a particular subscriber."

In the area of Web Services management, a new "common Web services management specification" is being developed by HP, IBM, Intel, and Microsoft. This new specification composes WS-ResourceTransfer and WS-EventNotification, building on the joint work in the area of information distribution and event notification.

According to the roadmap, the "reconciliation of the resource management and event/notification specifications enable reconciliation of many of the functions of the management specifications, including manipulation of state of managed resources (with sub-elements) and notification of management events and resource state change. The new set of management specifications should include support for the following features for metadata, including resource type information, to include bootstrapping the discovery process, discovery of the compliance levels and capabilities of the services and implementations, discovery and enumeration of resource types and the associated metadata, read/write access to the type space and associated metadata, navigation of relationships through the type and metadata space, accommodating a read-only type and metadata space which can be hosted outside the service and adapted to the actual service at runtime, and bootstrapping the discovery and enumeration of instances and event sources."

Authors of the roadmap document "expect the [above] specifications to be published and refined over the next 18-24 months; some of these specifications will be published as early as 2Q06. The specifications will be refined using the WS-* workshop process, with submission to a standards organization following that process when appropriate quality is assured."

The three 2004 WS-* specifications submitted to W3C convey the suggestion that "the Consortium make the submission[s] available for consideration by members or other third parties", with the note "To help with this work, we expect to be able to provide assistance as needed to the Consortium." W3C Team Comment on the submissions says that the W3C Web Services Coordination Group will be notified, and additional commentary is provided for each.

Bibliographic Information

W3C Team Comment

Comment on the three specifications submitted to W3C has been provided by Hugo Haas, Team Contact for W3C Web Services Coordination Group. Excerpts:

  • WS-Transfer

    WS-Transfer is a SOAP-based protocol for manipulating resources and their representations. One can create, modify, delete resources, as well as retrieve representations of those resources.

    Resources are defined as entities addressable by an endpoint reference that provide an XML representation. For the purpose of creating new resources, resource factories are introduced, defined as Web services that can create a new resource from an XML representation.

    This protocol is built using the SOAP messaging framework, both version 1.1 which is a W3C Member Submission and version 1.2 which is a W3C Recommendation, and the WS-Addressing Member Submission. It does not define, however, a URI to identify the SOAP module defined as per the SOAP 1.2 specification.

    There is an obvious parallel between WS-Transfer and the Hypertext Transfer Protocol (HTTP/1.1) and the Web itself: (1) concept of resources which are manipulated via representations, similar to Web resources; (2) the operations on resources are similar, with the WS-Addressing [action] property corresponding to the HTTP method: [a] HTTP GET versus Get Web service operation; [b] HTTP PUT versus Put Web service operation; [c] HTTP DELETE versus Delete Web service operation; [d] a Create Web service operation to enable resource creation corresponding to HTTP 201 responses following an HTTP POST or PUT.

    WS-Transfer can therefore be seen as an underlying protocol-independent version of HTTP, i.e. bringing the capabilities and properties of the Web and HTTP in contexts where HTTP is not used. The use of WS-Transfer is not limited to non-HTTP transports, and can also be used when HTTP is used as a communication tunnel. While the resources manipulated are entities that provide an XML representation, the use of the SOAP Message Transmission Optimization Mechanism along with WS-Transfer would allow one to efficiently manipulate other types of entities such as binary ones.

    However, there is one important difference between WS-Transfer resources and Web resources: their identification. While resources are identified by URIs on the Web as explained in section 2 of the Architecture of the World Wide Web, Volume One, WS-Transfer identifies them with endpoint references as defined by the WS-Addressing Member Submission, which means that WS-Transfer resources are potentially identified by more than just a URI, making them unsuitable for referencing and use in other Web technologies, e.g., in the context of traditional Web links or RDF assertions...

    WS-Transfer does not have all the features of HTTP regarding the manipulation of representations, such as caching, or content and language negotiation. However, the extensibility of SOAP would allow to add such capabilities incrementally, and it can benefit from the use of existing SOAP extensions such as WS-Security for security, or WS-Reliability or WS-Reliable Messaging for reliability..."

  • WS-Eventing

    WS-Eventing is a SOAP-based protocol to subscribe to notifications. The subscriber receives event messages from an event source, and can manage its subscription with a subscription manager.

    This protocol is built using the SOAP messaging framework, both version 1.1 which is a W3C Member Submission and version 1.2 which is a W3C Recommendation. It does not define, however, a URI to identify the SOAP module defined as per the SOAP 1.2 specification.

    The protocol also uses the WS-Addressing Member Submission, on which the Web Services Addressing Working Group has based WS-Addressing 1.0. In particular, the concept of endpoint references (EPR) defined is WS-Addressing is used to communicate the addresses of the subscriber, event source, and subscription manager.

    A subscription corresponds to a subscription manager EPR, i.e., WS-Eventing does not define as part of its protocol the concept of subscription identifier in its protocol. Should a Web service act as a subscription manager for more than one subscriptions, the specification defines a wse:Identifier element of type xs:anyURI to be used as a reference parameter in the subscription manager EPR. It might have been useful to have this concept part of the protocol to allow identification of subscriptions in other contexts.

    The delivery mode of the notification messages is open. The specification defines a Push mode, which is delivery mechanism where the source sends event messages to the sink as individual, unsolicited, asynchronous SOAP messages. The XML Protocol Working Group is working on a one-way underlying protocol binding for SOAP 1.2 which will allow such delivery over HTTP...

  • WS-Enumeration

    WS-Enumeration is a SOAP-based protocol for XML elements that is suitable for traversing logs, message queues, or other linear information models.

    This protocol is built using the SOAP messaging framework, both version 1.1 which is a W3C Member Submission and version 1.2 which is a W3C Recommendation. It does not define, however, a URI to identify the SOAP module defined as per the SOAP 1.2 specification.

    The core concept of this protocol is an enumeration context, which allows the data source to provide a session abstraction [...] to a consumer that represents a logical cursor through a sequence of data items. WS-Enumeration supports similar expiration and filtering capabilities as WS-Eventing, also submitted as a W3C Member Submission...

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