Contents

• Summary
• Bibliographic Information
• About WS-Eventing Version 2004-08
• Summary from IBM: WS-Eventing and WS-Notification
• Related Specifications
• Clogs and Bommentary
• Principal References

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 2004-08-30 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.

The new version of WS-Eventing "includes improvements such as the use of endpoint references in place of subscription ID which will enhance interoperability, new delivery modes that allow events to be pushed asynchronously, and addition of extensibility points to allow the possibility of adding other modes in the future."

According to Microsoft's summary: "Incorporating feedback from workshops and three new co-authors, this updated version of WS-Eventing defines a way for Web services to subscribe to or accept subscriptions for event notification messages generated by other Web services. WS-Eventing describes how to construct an event-oriented message exchange pattern using WS-Addressing concepts, allowing Web services to act as event sources for subscribers. It defines the operations required to manage subscriptions to event sources, as well as how the actual event messages are constructed."

A summary statement from IBM characterizes WS-Eventing 2004-08 as a specification which "supports the simplest levels of Web services interfaces for notification producers and consumers for a distributed event management system. The WS-Notification specifications (WS-BaseNotification, WS-BrokeredNotification, WS-Topics), by contrast, "provide a rich set of functions supporting publish/subscribe required by robust, scalable enterprise applications including message brokering and topic based subscription management."

WS-Eventing is designed as part of the WS-* composable architecture , viz., intended 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."

Other WS-* specifications referenced in WS-Eventing include Web Services Addressing (WS-Addressing), Web Services Policy Framework (WS-Policy), Web Services Reliable Messaging Protocol (WS-ReliableMessaging), Web Services Secure Conversation Language (WS-SecureConversation), Web Services Security: SOAP Message Security 1.0, Web Services Security Policy Language (WS-SecurityPolicy), Web Services Trust Language (WS-Trust), and Web Services Metadata Exchange (WS-MetadataExchange).

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."

Bibliographic Information

• Web Services Eventing (WS-Eventing). August [30] 2004. 38 pages. Copyright (c) 2004 BEA Systems Inc., Computer Associates International Inc., International Business Machines Corporation, Microsoft Corporation, Inc, Sun Microsystems, Inc, and TIBCO Software Inc. By Don Box (Microsoft), Luis Felipe Cabrera (Microsoft), Craig Critchley (Microsoft), Francisco Curbera (IBM), Donald Ferguson (IBM), Alan Geller (Editor, Microsoft), Steve Graham (IBM), David Hull (TIBCO Software), Gopal Kakivaya (Microsoft), Amelia Lewis (TIBCO Software), Brad Lovering (Microsoft), Matt Mihic (BEA Systems), Peter Niblett (IBM), David Orchard (BEA Systems), Junaid Saiyed (Sun Microsystems), Shivajee Samdarshi (TIBCO Software), Jeffrey Schlimmer (Microsoft), Igor Sedukhin (Computer Associates), John Shewchuk (Microsoft), Bill Smith (Sun Microsystems), Sanjiva Weerawarana (IBM), and David Wortendyke (Microsoft).

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

• Previous version: 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. 31 pages (PDF). Copyright (c) 2004 BEA Systems Inc., Microsoft Corporation, and Tibco Software Inc.

  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)."

About WS-Eventing Version 2004-08

"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." The Web Services Eventing (WS-Eventing) specification provides for this mechanism with subscription/notification facilities. "To improve robustness, a subscription may be leased by an event source to a subscriber, and the subscription expires over time. The subscription manager provides the ability for the subscriber to renew or cancel the subscription before it expires."

Requirements. The specification intends to meet the following requirements:

• Define means to create and delete event subscriptions
• Define expiration for subscriptions and allow them to be renewed
• Define how one Web service can subscribe on behalf of another
• Define how an event source delegates subscription management to another Web service
• Allow subscribers to specify how event messages should be delivered
• Leverage other Web service specifications for secure, reliable, transacted message delivery
• Support complex eventing topologies that allow the originating event source and the final event sink to be decoupled
• Provide extensibility for more sophisticated and/or currently unanticipated subscription scenarios
• Support a variety of encoding formats, including (but not limited to) both SOAP 1.1 and SOAP 1.2 Envelopes

WS-Eventing Terminology

• Delivery Mode: The mechanism by which event messages are delivered from the source to the sink
• Event Source: A Web service that sends notifications and accepts requests to create subscriptions
• Event Sink: A Web service that receives notifications
• Notification: A one-way message sent to indicate that an event has occurred
• Push Mode: A delivery mechanism where the source sends event messages to the sink as individual, unsolicited, asynchronous SOAP messages
• Subscriber: A Web service that sends requests to create, renew, and/or delete subscriptions
• Subscription Manager: A Web service that accepts requests to manage get the status of, renew, and/or delete subscriptions on behalf of an event source

Delivery Modes. "While the general pattern of asynchronous, event-based messages is extremely common, different applications often require different event message delivery mechanisms. For instance, in some cases a simple asynchronous message is optimal, while other situations may work better if the event consumer can poll for event messages in order to control the flow and timing of message arrival. Some consumers will require event messages to be wrapped in a standard "event" SOAP envelope, while others will prefer messages to be delivered unwrapped. Some consumers may require event messages to be delivered reliably, while others may be willing to accept best-effort event delivery.

In order to support this broad variety of event delivery requirements, the WS-Eventing specification introduces an abstraction called a Delivery Mode. This concept is used as an extension point, so that event sources and event consumers may freely create new delivery mechanisms that are tailored to their specific requirements. This specification provides a minimal amount of support for delivery mode negotiation by allowing an event source to provide a list of supported delivery modes in response to a subscription request specifying a delivery mode it does not support. This specification defines a single delivery mode, Push Mode, which is simple asynchronous messaging..."

Subscription Managers. "In some scenarios the event source itself manages the subscriptions it has created. In other scenarios, for example a geographically distributed publish-and-subscribe system, it may be useful to delegate the management of a subscription to another Web service. To support this flexibility, the response to a subscription request to an event source will include the EPR [endpoint reference] of a service that the subscriber may interact with to manage this subscription. This EPR should be the target for future requests to renew or cancel the subscription. It may address the same Web service (Address and ReferenceProperties) as the event source itself, or it may address some other Web service to which the event source has delegated management of this subscription; however, the full subscription manager EPR (Address and Reference Properties and ReferenceParameters) must be unique for each subscription. We use the term "subscription manager" in the WS-Eventing specification to refer to the Web service that manages the subscription, whether it is the event source itself or some separate Web service..."

New Appendix — 'Service Metadata for Eventing'. "In order to obtain the event-related metadata that describes a service, the mechanisms described in WS-MetadataExchange should be used. The GetMetadata operation defined there allows WSDL and policy information to be retrieved. The WSDL will contain annotations that identify a service as an event source and that identify those messages that describe notification messages. The policy will specify the delivery modes and filter types supported by the event source...

To indicate that notification and solicit-response operations within a WSDL 1.1 portType are events exposed by an event source, this specification defines an @wse:EventSource attribute to annotate the portType for the event source. The normative outline for the @wse:EventSource attribute is provided... As described here, to subscribe to events exposed by an event source, a subscribing endpoint sends a Subscribe message to the endpoint reference for the event source. If the Subscribe does not include a filter, the event sink should expect to receive events defined by notification operations within the portType and should expect to receive and respond to events defined by solicit-response operations within the portType. [The editors] anticipate that this WSDL extension may change in subsequent versions of this specification..." An example WSDL 1.1 description is provided for a hypothetical storm warning service that exposes a wind report event. [On WS-MetadataExchange, see "Web Services Metadata Exchange for Service Endpoints."]

Summary from IBM: WS-Eventing and WS-Notification

Web Services Eventing (WS-Eventing) "defines how Web Services Eventing supports the simplest levels of Web services interfaces for notification producers and consumers for a distributed event management system.

The WS-Eventing specification defines a baseline set of operations that allow Web services to provide asynchronous notifications to interested parties. WS-Eventing defines the simplest level of Web services interfaces for notification producers and notification consumers including standard message exchanges to be implemented by service providers that wish to act in these roles, along with operational requirements expected of them.

WS-Eventing specification provides similar functionality to that of WS-BaseNotification. WS-BaseNotification is one of the WS-Notification specifications that were submitted to an OASIS TC in April 2004. The WS-Notifications specifications provide a rich set of functions supporting publish/subscribe required by robust, scalable enterprise applications including message brokering and topic based subscription management.

IBM joined the WS-Eventing author group to support the interoperability requirements of our customers by driving work to align the two specifications and reduce potential for overlap and incompatibilities. The new version of WS-Eventing includes improvements such as the use of endpoint references in place of subscription ID which will enhance interoperability, new delivery modes that allow events to be pushed asynchronously, and addition of extensibility points to allow the possibility of adding other modes in the future..." [from the IBM WS-Eventing reference page]

Related Specifications

• WS-Notification from the OASIS Web Services Notification Technical Committee:

  • Web Services Base Notification Version 1.2 (WS-BaseNotification). Working Draft 03. 21-June-2004. "The Event-driven, or Notification-based, interaction pattern is a commonly used pattern for inter-object communications. Examples exist in many domains, for example in publish/subscribe systems provided by Message Oriented Middleware vendors, or in system and device management domains. This notification pattern is increasingly being used in a Web services context. This document defines the Web services interfaces for NotificationProducers and NotificationConsumers. It includes standard message exchanges to be implemented by service providers that wish to act in these roles, along with operational requirements expected of them. This is the base specification on which the other WS-Notification specification documents depend. An implementer interested just in direct, point to point, notification need only read this WS-BaseNotification specification, together with the Publish-Subscribe Notification for Web Services white paper..."
  • Web Services Brokered Notification Version 1.2 (WS-BrokeredNotification). Working Draft 01. 21-July-2004 . "This specification defines the Web services interface for the NotificationBroker. A NotificationBroker is an intermediary, which, among other things, allows publication of messages from entities that are not themselves service providers. It includes standard message exchanges to be implemented by NotificationBroker service providers along with operational requirements expected of service providers and requestors that participate in brokered notifications. This work relies upon WS-Base Notification and WS-Topics, as well as the Publish-Subscribe Notification for Web Services document..."
  • Web Services Topics Version 1.2 (WS-Topics). Working Draft 01, 22-July-2004. "This document defines a mechanism to organize and categorize items of interest for subscription known as 'topics'. These are used in conjunction with the notification mechanisms defined in WS-Base Notification. WS-Topics defines three topic expression dialects that can be used as subscription expressions in subscribe request messages and other parts of the WS-Notification system. It further specifies an XML model for describing metadata associated with topics. This specification should be read in conjunction with the WS-Base Notification specification and the Publish-Subscribe Notification for Web Services document."

• WS-Events from Hewlett-Packard:

  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)."

Clogs and Bommentary

• "I wonder what's going on behind the scenes. The new version of WS-Eventing has IBM as a co-author. What does this suggest about WS-Notification? Could it be the case that WS-Eventing is going to be layered underneath WS-Notification or are we going to see the two merging? Also, the ID of the subscription has become an EPR!!! This means that the ID of a subscription is coupled, if used, with the endpoint of the subscription manager service, which is remarkably similar to the way WS-RF does things. Instead of carrying the identification of the subscription in the body of the message, it is expected that event sinks will return an EPR with the 'appropriate' reference properties or parameters to identify the subscription.The information from the EPR is used with every communication regarding the particular subscription. Also, an example where a custom dialect for filtering on topics is given. This reminds me of WS-Topics..." (Savas Parastatidis)

• "The WS-Eventing specification defines a baseline set of operations that allow Web services to provide asynchronous notifications to interested parties. WS-Eventing defines the simplest level of Web services interfaces for notification producers and notification consumers including standard message exchanges to be implemented by service providers that wish to act in these roles, along with operational requirements expected of them. WS-Eventing specification provides similar functionality to that of WS-BaseNotification. WS-BaseNotification is one of the WS-Notification specifications that were submitted to an OASIS TC in April 2004. The WS-Notifications specifications provide a rich set of functions supporting publish/subscribe required by robust, scalable enterprise applications including message brokering and topic based subscription management. IBM joined the WS-Eventing author group to support the interoperability requirements of our customers by driving work to align the two specifications and reduce potential for overlap and incompatibilities. The new version of WS-Eventing includes improvements such as the use of endpoint references in place of subscription ID which will enhance interoperability, new delivery modes that allow events to be pushed asynchronously, and addition of extensibility points to allow the possibility of adding other modes in the future..." (Summary from IBM on WS-Eventing and WS-Notification)

• "It seems like the more work that is done to simplify Web services standardization, the more confusing it gets. This week, IBM, Sun Microsystems and Computer Associates got behind the Microsoft-driven WS-Eventing specification supporting publish-and-subscribe Web services functionality. But IBM still touts its own rival WS-Notification specs as its preferred route while saying the company will enable interoperability with WS-Eventing. IBM wrote, 'WS-Eventing specification provides similar functionality to that of WS-BaseNotification. WS-BaseNotification is one of the WS-Notification specifications that were submitted to an OASIS [technical committee] in April 2004..." (Paul Krill)

• "The Web Services workshops are working at full effort, specs are coming through, all the major vendors are not only participating but also publicly taking firm postions of support from the CEO level down. By the time all the WS specs get out of workshops, which I blogged on earlier, there's going to be a good quality of standard spec with proven interop between the major market vendors before everyone can use these specs royalty free common use... The updated WS-Eventing spec has new industry feedback out of feedback and interoperability Web Service workshops. With the new enhancements, higher level specifications such as WS-Notification that layer on top of WS-Eventing should improve their prospects for syntactical interop for customers..." (Dave Welsh)

• "IBM has had a similar specification to WS-Eventing, called WS-BaseNotification, which was submitted to OASIS in April as part of IBM's WS-Notification specifications submission. But IBM's participation in WS-Eventing does not spell the end for WS-BaseNotification and WS-Notification. In fact, the company still plans to support its WS-Notification specifications to enable publish-subscribe functionality for Web services in its WebSphere application server, said Karla Norsworthy, director of dynamic business technologies at IBM. The company's products, however, will be able to communicate with systems that use WS-Eventing, she said. 'We decided the best [choice] for us was to drive these [specifications] close together, but it doesn't change our commitment to WS-Notification at all,' Norsworthy said. Over the long term, IBM would like to see WS-Eventing converged with its own technologies into one specification. 'I think as a long-term strategy, we'd love to see that, but at this point, we're trying to make sure that we can factor these things [so] that it's easy for them to work together in customer environments that end up with both of them,' Norsworthy said. WS-Notification supports intermediary brokering technologies for publish-and-subscribe Web services paradigms, but WS-Eventing currently does not..." (Karla Norsworthy)

• "Sun [Microsystems] recognizes that customers are best served when the industry engages in constructive collaboration on web services. The joint work on WS-Eventing is complimentary to our ongoing collaboration with Microsoft and is the latest step as we continue to converge our efforts in web services. We consider WS-Eventing a valuable foundation in our objective to provide seamless computing in a heterogeneous computing environment. Sun will continue to seek opportunities which will enable customers to build web services solutions that interoperate across platforms..." (Jacki DeCoster)

• Sun comment arguably relevant ["this space"] to WS-Eventing 2004-08 given that the new WS-Eventing draft is revised to align it more explicitly with WS-Addressing, for which Sun Microsystems signed on to participate as an author. "'Our customers are interested in a single set of standards in this space,' says Bill Smith, Sun's director of software standards. 'We're joining our competitors in supporting this specification because our customers want products that interoperate. The best way to achieve that is through a set of open standards. We saw this as an opportunity to help influence that process and get things into an open organization like the W3C and eventually end up with a single standard in the addressing space. That's good for all concerned..." (Bill Smith)

• "Microsoft and others published an update to the WS-Eventing specification. The bigger news is that IBM and Sun are co-authors on this update. For those who thought IBM and Msft were breaking ties when IBM was not on the original draft, I can say this is a good sign that we are still working closely together. I'm also happy to see Sun added to the list of authors. Its good to see them not only involved in the future direction of Web services, but also working with all the companies in the Workshop process to get their input on the specs in so that the process of getting these ratified by standards bodies will be a lot more efficient and focused. Of course the real take-away here is that the industry is dedicated toward the advancement of the Web service architecture. The fact that three companies agreed on the spec is nominal compared to the fact that three companies, that disagree on many things including some of their views on the future of Web services, believe moving the Web service architecture forward is a really big deal and are dedicated to working together to make sure that happens..." (Matt Powell)