Web Services Choreography Description Language (WS-CDL)

April 19, 2012

The Web Services Choreography Description Language (WS-CDL) is a W3C candidate recommendation. It is a language for describing how peer-to-peer participants’ collaborate.1 In this shared environment, the computer network can act as a client or server for the other computers in the network. This allows shared access to files and devices connect to host computers, without the need for a central server. Each network type needs all computers in the network to use the same or a compatible program to connect to each other. Audio, data, video or anything in digital format can be shared. Further in this article, a discussion of WS-CDL and its impact on business processes will take place.

Activities that involve different organizations or independent processes are engaged in a collaborative fashion to achieve a common business goal, such as order fulfillment or data sharing. For the collaboration to work properly, the rules of assignation between all the interacting participants must be provided. The WS-CDL is aimed at being able to describe collaborations between any type of participant, regardless of the supporting platform or programming model used by the implementation of the hosting environment.

Using the WS-CDL, a contract containing a "global" definition of the common ordering conditions and constraints under which messages are exchanged, is produced that describes, from a global viewpoint, the common and complementary observable behavior of all the participants involved. Each participant can then use the global definition to build and test solutions that conform to it. The global specification is in turn realized by a combination of the consequential local systems, on the basis of appropriate infrastructure support.

In real-world scenarios, companies are often unwilling to delegate control of their business processes to their integration partners. WS-CDL offers a means by which the rules of participation within collaboration can be clearly defined and agreed to, collectively. Each part may then implement its portion of the choreography as determined by the common agreed view.

The figure below demonstrates a possible usage of WS-CDL.

Company A Company B

In Figure 1, Company A and Company B wishes to integrate their Web Services based applications. The respective business analysts at both companies agree upon the services involved in the collaboration, their interactions, and their common ordering and constraint rules under which the interactions occur. They then generate a WS-CDL based representation. In this example, choreography specifies the interactions between services across business entities ensuring interoperability, while leaving actual implementation decisions in the hands of each individual company:

  • Company "A" relies on a WS-BPEL3 solution to implement its own part of the choreography
  • Company "B", having greater legacy driven integration needs, relies on a J2EE4 solution incorporating Java and Enterprise Java Bean Components or a .NET5 solution incorporating C# to implement its own part of the choreography2

More specifically, the goals of the WS-CDL specification are to permit: Reusability, Cooperation, Multiple party, Ability to compose, information alignment, transactional and Information Driven collaboration of shared resources.

This type of peer-to peer participation collaboration is a method used with six sigma and lean initiatives throughout many industries. WS-CDL is enabling companies to save money, time and eliminate bottlenecks in their business processes. What do I mean by bottlenecks? These are simply the limiting steps in a process. Bottlenecks destroy productivity. Bottlenecks are the perfect example of a small change that can have a huge impact on your productivity. If an activity takes four hours, but three are spent on just one step, speeding up that step could make a system 7 times more productive. With the use of WS-CDL, each trust entity on a network can see each other’s files, share information and greatly decrease data loss. Over-all WS-CDL can make a corporation run more efficiently and is increasingly utilized because of its great benefits.

Ronique Carter


2 Responses to “Web Services Choreography Description Language (WS-CDL)”

  1. Krishnan Iyer said

    Good Post Ronique. The WS-CDL and BPEL complement each other and can co-exist.

  2. Frank Brown said

    I was curious how WS-CDL tied into other Web Service languages and I found the following Artical which gives us more information on the topic:

    Web Services Choreography Description Language Version 1.0

    Relationship with XML and WSDL
    The WS-CDL specification depends on the following specifications: XML 1.0 [XML], XML-Namespaces [XMLNS], XML-Schema 1.0 [XMLSchemaP1], [XMLSchemaP2] and XPointer [XPTRF]. Support for including and referencing service definitions given in WSDL 2.0 [WSDL20] is a normative part of the WS-CDL specification. In addition, support for including and referencing service definitions given in WSDL 1.1 as constrained by WS-I Basic Profile [Action: add references] is a normative part of the WS-CDL specification.

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