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Building a real-world Web service-part 2: choreography--making Web services dance. (Enterprise Solutions).

Article Excerpt
No, Web services isn't just hype. This series of articles will show you that Web services are real and can provide great benefits to organizations today. The series demonstrates how to build a real-world Web service by combining the features of Web services with components and knowledge of RosettaNet, an industry leader in e-business process standards.

I use WSDL (Web Service Description Language) and BPEL4WS (Business Process Execution Language for Web Services) to create Web services definitions for RosettaNet PIPs (Partner Interface Processes), and then use BPWS4J (Business Process Execution Language for Java Runtime) to implement these definitions. In this article, I will define the choreography for the real-world Web service by creating a BPEL4WS process that utilizes the Web service defined in Part 1. This article is all about choreographing the e-business dialogue, so put on your dancing shoes ... the party's just begun.

Add a Little BPEL

In Part 1 (Vol. 4, issue 2), I showed you how to build a WSDL definition for a RosettaNet PIP. Along the way I discussed the true value of Web services, which is revealed in how they enable organizations to focus on services, and provide partners and customers access to these services through open and accessible public interfaces. I also talked about e-business dialogues and how to use the RosettaNet specification in Web services to conduct them. I ended the article by building a WSDL definition of the purchase order PIP from RosettaNet. In this installment, I'll take the real-world Web service definition further by adding BPEL4WS (written as BPEL from this point on) to the mix and defining an abstract process based on the WSDL definition. This abstract process will serve as a basis of the e-business dialogue definition that business partners will use to conduct e-business.

I need to add choreography definitions to the e-business dialogue I'm building for the real-world Web service. The choreography will describe how processes and partners will interact with each other. These interactions exceed the limited functionality offered by the message exchange patterns available in the WSDL, which is why I'm using BPEL to pick up where WSDL left off.

The choreography information is central to the e-business dialogue, and there is a strong need for choreography languages tO compose standard messages into meaningful, long-running e-business dialogues that can be used to conduct complete business scenarios. Choreography languages become more relevant as organizations begin to conduct e-business through their digital representations; it's simply not enough to have common message definitions (like those specified by EDI) and leave the choreography aspect of the dialogue to be handled over the phone or in face-to-face meetings. E-business dialogues are about interactions between digital representations of the business, and these representations need concrete choreography definitions (see Figure 1).

[FIGURE 1 OMITTED]

The Digital Representation of a Business

I have been talking about creating e-business dialogues between business partners. In my informal definition of the term, an e-business dialogue is two or more partners accomplishing a business goal (e.g., buying and selling goods) by conducting a dialogue between their...

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