Update: August 31, 2004 BEA, CA, IBM, Microsoft, Sun, and Tibco Release Updated WS-Eventing Specification.     A revised version of the Web Services Eventing (WS-Eventing) specification has been published by BEA Systems Inc., Computer Associates International Inc., International Business Machines Corporation, Microsoft Corporation, Inc, Sun Microsystems, Inc, and TIBCO Software Inc. This draft version provided for public review and evaluation updates the earlier draft of WS-Eventing released by BEA, Microsoft, and TIBCO in January 2004. The WS-Eventing specification describes a protocol that allows Web services to subscribe to or accept subscriptions for event notification messages. It defines a single delivery mode, Push Mode, which is simple asynchronous messaging. WS-Eventing is designed as part of the WS-* composable architecture , viz., intended to to be composed with other WS-* specifications "to provide a rich set of tools to provide security in the Web services environment; the specification specifically relies on other Web service specifications to provide secure, reliable, and/or transacted message delivery and to express Web service and client policy." WS-Eventing "defines a protocol for one Web service (called a 'subscriber') to register interest (called a 'subscription') with another Web service (called an 'event source') in receiving messages about events (called 'notifications' or 'event messages'). The subscriber may manage the subscription by interacting with a Web service (called the 'subscription manager') designated by the event source." While many mechanisms are available by which event sources may deliver events to event sinks, the WS-Eventing specification "provides an extensible way for subscribers to identify the delivery mechanism they prefer. While asynchronous, pushed delivery is defined in WS-Eventing, the intent is that there should be no limitation or restriction on the delivery mechanisms capable of being supported by this specification."

[January 07, 2004] A draft version of Web Services Eventing (WS-Eventing) has been published as a new member of the 'Composable Architecture' (WS-*) Web service specifications. The WS-Eventing specification "describes a protocol that allows Web services to subscribe to or accept subscriptions for event notification messages." An example request to create a subscription for storm warnings is used to illustrate the notification protocol. "Web services often want to receive messages when events occur in other services and applications. A mechanism for registering interest is needed because the set of Web services interested in receiving such messages is often unknown in advance or will change over time." Formal models for the protocol are provided in the XML Schema and WSDL files. Supporting both SOAP 1.1 and SOAP 1.2 Envelopes, the specification intends to define a "means to create and delete event subscriptions, to define expiration for subscriptions, and to allow them to be renewed. It defines how an event sink can determine which subscriptions it is receiving notifications for, and how one event sink can subscribe on behalf of another. The specification is meant to leverage other Web service specifications for secure, reliable, transacted message delivery. It provides extensibility for more sophisticated and/or currently unanticipated subscription scenarios."

Bibliographic Information

Web Services Eventing (WS-Eventing). By Luis Felipe Cabrera (Microsoft), Craig Critchley (Microsoft), Gopal Kakivaya (Microsoft), Brad Lovering (Microsoft), Matt Mihic (BEA Systems), David Orchard (BEA Systems), Shivajee Samdarshi (TIBCO Software), Jeffrey Schlimmer (Editor, Microsoft), John Shewchuk (Microsoft), and David Wortendyke (Microsoft). January 2004. Copyright (c) 2004 BEA Systems Inc., Microsoft Corporation, and Tibco Software Inc. 31 pages (PDF).

Acknowledgements: "This specification has been developed as a result of joint work with many individuals and teams, including: Don Box (Microsoft), Josh Cohen (Microsoft), Geary Eppley (Microsoft), Omri Gazitt (Microsoft), Peter Jarvis (Microsoft), Chris Kaler (Microsoft), Amy Lewis (TIBCO Software), Toby Nixon (Microsoft), Denny Page (TIBCO Software), Anders Vinberg (Microsoft), Alex Weinert (Microsoft)."

WS-Eventing: Summary

Introduction: "Web services often want to receive messages when events occur in other services and applications. A mechanism for registering interest is needed because the set of Web services interested in receiving such messages is often unknown in advance or will change over time. This specification defines a protocol for one Web service (called an "event sink") to register interest (called a "subscription") with another Web service (called an "event source") in receiving messages about events (called "notifications"). To improve robustness, the subscription is leased by an event source to an event sink, and the subscription expires over time. An event source may allow an event sink to renew the subscription.

Terminology:

• Notification: A one-way message sent to indicate that an event has occurred.
• Event Source: A Web service that sends notifications and accepts requests to create, renew, and delete subscriptions.
• Event Sink: A Web service that receives notifications and/or sends requests to create, renew, and/or delete subscriptions.
• Subscribing Event Sink: An event sink that sends request to create, renew, and/or delete subscriptions, perhaps on behalf of another event sink.

Subscription Messages: To create, renew, and delete subscriptions, subscribing event sinks send request messages to event sources. When an event source accepts a request to create a subscription, it does so for a given amount of time. If the event source accepts a renewal request, it updates that amount of time. During that time, notifications are sent by the event source to the requested destination. An event source may support filtering to limit notifications that are sent to the event sink; if it does and a subscribe request contains a filter, the event source sends only notifications that match the requested filter. The event source sends notifications until one of the following happens: the event source accepts an unsubscribe request for the subscription, the subscription expires without being renewed, or the event source cancels the subscription prematurely. Finally, the event source makes a best effort to indicate why the subscription ended..."

Composable Architecture: "By using the XML, SOAP, and WSDL extensibility models, the Web service specifications (WS-*) are designed to be composed with each other to provide a rich set of tools to provide security in the Web services environment. This specification specifically relies on other Web service specifications to provide secure, reliable, and/or transacted message delivery and to express Web service and client policy..." [excerpted from the 2004-01 draft spec]

Related Specification: WS-Events

In July 2003, HP announced the publication of a Web Services Management Framework Version 2.0 and plans to contribute the specification set to the OASIS Web Services Distributed Management TC. The WS-Events component in this framework defines the Web services based event notification mechanism and is used by WSMF-Foundation:

Web Services Events (WS-Events) Version 2.0. Edited by Nicolas Catania (Hewlett-Packard Company). 16 July 2003. 23 pages. Authors: Pankaj Kumar (Hewlett-Packard Company), Bryan Murray (Hewlett-Packard Company), Homayoun Pourhedari (Hewlett-Packard Company), William Vambenepe (Hewlett-Packard Company), and Klaus Wurster (Hewlett-Packard Company). See also the WS-Events XML schema and WS-Events WSDL.

"This document describes Web Services Events (WS-Events) Version 2.0, an XML syntax and a set of processing rules for advertising, subscribing, producing and consuming Web Services Events. An Event is an abstract concept that is physically represented by a Notification. Notifications flow from Event producer to Event consumer using asynchronous or synchronous delivery modes (push/pull)."