The light-gray use cases are all related to process workflow and messaging. When coordinating the activities of business partners in a B2B application, shared process definitions are as important as shared vocabularies. The business process definition describes how and when business documents (based on the shared vocabularies) are exchanged, and the workflow model automates those processes by assigning activities to workers. Message protocols define agreements used to control conversation between two or more agents.

　　The dark-gray use cases represent requirements for application integration. The creation of application classes can often be automated based on either the vocabulary definition or the XML schema. The details of legacy system adapter creation vary widely and are determined by platform, architecture, middleware, vendor APIs and so on. At this high-level view, the System Integration Specialist is responsible for ensuring that these adapters are able to import and export XML messages conforming to the required schemas and are compatible with the message protocols used by the workflow.

　　When reviewing the overall use case diagram, notice that all requirements depend on the "Define Business Vocabulary" use case. In application environments in which the XML vocabulary is provided by an outside entity, development activities are driven by that definition.

　　XML Vocabulary Development Process

　　A vocabulary definition is the heart and soul of an XML application, but there's no single right way to create it. What's more, many applications share parts of larger XML vocabulary definitions without requiring the entire schema. This modularity of XML vocabulary design—implemented via the XML namespace standard—is essential for enabling reuse across a range of applications, just as good object-oriented design is essential for enabling class and component reuse. When XML vocabularies are designed using UML class, package and component diagrams, it becomes much easier to apply similar concepts of reuse to both XML and object technology.

　　Commerce One's XML Common Business Library (xCBL), designed to support B2B e-commerce (www.xcbl.org), provides a good example of an XML vocabulary. Like many contemporary XML schemas, the xCBL vocabulary is defined using one very large namespace of elements. (This is because many schemas were developed prior to completion of the XML namespace standard and its support in development tools.) The modularity of its components is not explicit, but is informally (and incompletely) annotated with comments in the schema file. There is, however, a set of core element definitions that are reused in several other message types; for example, Catalog, Trading Partner, Auction, Order and Invoice.

　　I have reverse engineered several modules from the xCBL 3.0 schema into UML class diagrams, which are now used by the OASIS Universal Business Language (UBL) technical committee (http://oasis-open.org/committees/ubl) to assist review and redesign of the xCBL XML vocabulary as part of an open standards process. One of the primary goals of this redesign effort is to specify the vocabulary as part of the emerging ebXML core components library (http://www.ebxml.org).

　　The class diagram entitled XML Vocabulary Model From xCBL Schema (below) represents a very small subset of xCBL, showing several identification elements from the core module and their use within the TradingPartnerOrganizationHeader element. The header also includes other elements not shown here. I wrote an automated transformation from the SOX schema language used by xCBL to an XMI document conforming to UML 1.3, which I then imported into Rational Rose.

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