First Public WD: Web Services Choreography Description Language (WS-CDL)
World Wide Web Consortium Publishes First Public Working Draft of Web Services Choreography Description Language 1.0
W3C's WS-CDL Targets Peer-to-Peer Web Services Collaboration
W3C http://www.w3.org/ — 27 April 2004
The World Wide Web Consortium (W3C) has issued the Web Services Choreography Description Language Version 1.0 as a W3C First Public Working Draft. The Web Services Choreography Description Language (WS-CDL) is targeted to coordinate interactions among Web services and their users. This is the first in the series of WS-CDL drafts.
Choreography is the Key to Enterprise-Level Web Services
Business transactions, especially those envisioned by Web services, grow from complex interactions. These interactions can be viewed from a variety of points in the transaction chain, not simply the start or the expected endpoint. Modeling these interactions from a global viewpoint allows software developers to take into account the distributed race conditions (unexpected dependence on the sequence of events) that may exist — in much the same way they exist in non-Web business processes. Choreography provides the set of rules that explains how different components may act together, and in what sequence, giving a flexible systemic view of the process.
The Web Services Choreography Description Language is a necessary complement to end point languages such as BPEL and Java. WS-CDL provides them with the global model they need to ensure that end point behavior — the "rules of engagement" — is consistent across cooperating services.
Choreography Speeds Time to Market and Reduces Cost of Ownership
One of the aims of Web services is integration (combining components into a system) to reduce connectivity costs and increase the utility and thus the value of information. For many years, the only way integration could be achieved was to plug services together by custom-coding or "wiring" the integration points. Through the use of a global model, choreography ensures that contractual behavior across multiple services can be achieved without complex wiring or complex wiring tools.
Another Web services goal is conformance (the integration of applications so that they share the same rules of engagement) which ensures the desired business outcome. Because a well-defined choreography guarantees conformance across application domains, businesses gain faster time to market.
Statistically, choreography can be shown to be free from deadlocks (when processes stop because each is waiting for one of the others), livelocks (when processes continually react to each other and stop doing useful work) and leaks (interference from unauthorized participants). Leak freedom ensures greater security across connected services. The absence of deadlocks and livelocks lowers testing costs and reduces the total cost of ownership.
WS-CDL Defines Collaboration Between Applications
The WS-CDL specification defines peer-to-peer collaboration between Web service participants. A user of a Web service, automated or otherwise, is a "client" of that service. Users may be other Web services, applications and human beings. In WS-CDL, a set of client interactions may be related over time in a "collaboration group." A collaboration group could be for example, a set of components that make up a business transaction or a database transaction.
The future of e-business applications is in the loosely coupled, decentralized environment of the World Wide Web. This environment requires the ability to perform long-lived, peer-to-peer collaborations between the participating services, within or across the trusted domains of an organization. Applications that implement WS-CDL can accomplish this shared business goal, as the Working Group developed its requirements document to consider both broad practical business needs and sound theories.
WS-CDL Has Sound Industrial and Mathematical Foundations
The WS-CDL specification brings together important resources from both industry and research. WS-CDL incorporates not only business requirements, but also seminal mathematical work in pi calculus, an algebra based on naming used to model systems that are physically or virtually mobile. Invited Experts in the W3C Web Services Choreography Working Group include Professor Robin Milner, the principal creator of pi calculus; Dr. Kohei Honda; and Dr. Nobuko Yoshida. Their collective work on pi calculus and correctness properties (livelock, deadlock and leak freedom) is the underpinning of WS-CDL, giving the language mathematical soundness.
WS-CDL Moves into Full Development
In preparation for today's first public release, the W3C Web Services Choreography Working Group has already published Web Services Choreography requirements and its model overview last month. The Working Group designed this foundation for WS-CDL to be consistent with Web Services Architecture, and to augment the Architecture of the World Wide Web, First Edition, a work in progress by the W3C's Technical Architecture Group (TAG).
WS-CDL is XML-based and supports SOAP Version 1.2, WSDL 2.0, and the Web's architectural layers. As all W3C Web Services Working Groups are required to coordinate with each other to ensure a smooth and sound infrastructure, WS-CDL is designed to be interoperable with all deliverables in the W3C Web Services Activity.
The Web Services Choreography Working Group is now focusing its attention on refining WS-CDL, with the intention of developing early implementations. W3C invites the Web development community to review and comment on this publication and subsequent drafts. Technical discussion of WS-CDL is conducted publicly on the firstname.lastname@example.org mailing list.
Over 40 W3C Member Organizations and Invited Experts Are Building WS-CDL
The participants in the W3C Web Services Choreography Working Group (in alphabetical order) are Apple Computer; Arjuna Technologies Ltd; BEA Systems; Choreology Ltd; Cisco Systems; Commerce One; Computer Associates; DSTC Pty Ltd (CITEC); EDS; Enigmatec Corporation; Fujitsu Ltd; Hewlett-Packard; Hitachi, Ltd.; Intalio Inc.; IONA; MTA SZTAKI; National Computerization Agency; Nortel Networks; Novell; Oracle; SAP AG; SeeBeyond Technology Corporation; Software AG; Sonic Software; Sun Microsystems, Inc.; Thomson Corporation; TIBCO Software; Uniform Code Council; University of Maryland (Mind Lab); W. W. Grainger, Inc.; webMethods, Inc., and Invited Experts Dr. Honda, Professor Milner, and Dr. Yoshida. The group is chaired by Martin Chapman (Oracle) and Steve Ross-Talbot (Enigmatec).
About the World Wide Web Consortium (W3C)
The W3C was created to lead the Web to its full potential by developing common protocols that promote its evolution and ensure its interoperability. It is an international industry consortium jointly run by the MIT Computer Science and Artificial Intelligence Laboratory (MIT CSAIL) in the USA, the European Research Consortium for Informatics and Mathematics (ERCIM) headquartered in France and Keio University in Japan. Services provided by the Consortium include: a repository of information about the World Wide Web for developers and users, and various prototype and sample applications to demonstrate use of new technology. To date, nearly 400 organizations are Members of the Consortium. For more information see http://www.w3.org/
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Prepared by Robin Cover for The XML Cover Pages archive. See other details in the news story: "W3C Publishes Web Services Choreography Description Language (WS-CDL)." General references to choreography standards: "Messaging and Transaction Coordination."