9.6. Summary The main points of this chapter include the following: This chapter covers four important but peripheral BPM approaches: the OMG BPM metamodels, XLANG and WSFL, and BPSS. The OMG, best known for its CORBA standards, is an emerging BPM player, having recently published RFPs for the specification of abstract BPM models of process definition (BPDM) and process runtime interface (BPRI). More important than the RFP process and its current bids is the OMG's idea that BPM can have a model-driven architecture. In a nutshell, MDA, when applied to BPM, helps bridge the gap between disparate process languages by specifying a common foundationeither a MOF metamodel or a UML profileallowing BPDM-aware BPM tools to exchange particular process definitions more easily. For example, a BPMN tool can export a diagram as a BPMN XMI document, which can then be imported into a BPEL tool and transformed into a BPEL process definition. Microsoft's XLANG is an XML process definition language that is interesting for two reasons: its use of the pi-calculus (examined in Chapter 3) and its influence on BPEL. BPEL began as a synthesis of XLANG and IBM's WSFL. The XLANG contribution is its programmatic style of web services orchestrationusing familiar control structures such as all, while, and sequence, surrounding action steps that model web service interactionsand its global model, which resembles BPEL's partner link interface. XLANG is dead; Microsoft, as one of the principal BPEL authors, is now building to BPEL rather than to XLANG. IBM's WSFL, an XML process definition language that uses directed graphs rather than programmatic constructs to describe a process, is the other main influence on BPEL. The influence of the directed graph approach, as well as the concept of dead path elimination, is clearly seen in BPEL's flow construct. WSFL has both process-level orchestration, in which control links connect web services, as well as global orchestration, and plug links connect activities across the processes of multiple participants. WSFL is also interesting for its application of the Petri net, which is explored in Chapter 3. The precise communication of business partners in B2B ecommerce requires a stronger notion than choreography. In the ebXML BPSS, a collaboration is a set of precise, transactional message exchanges with legal and business trade ramifications. Each exchange is referred to as a business transaction, which begins when one party (e.g., a buyer) sends a request to another (e.g., a seller); the second party then acknowledges receipt and acceptance of the request and sends a response, for which the first party then acknowledges receipt. Choreography helps structure the flow of control from one transaction to another. For example, a buyer-seller relationship can be specified to be the sequence of Create Order and Notify Shipment TRansactions.
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