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Loosely Coupled weblog

Wednesday, December 03, 2003

Managing the unmapped
One of the most promising initiatives to define a standard for co-ordinating multiple autonomous processes is WS-CAF, (Web Services Composite Application Framework), which is currently in development care of OASIS.

Mark Little and Jim Webber of Arjuna Technologies, one of the vendors contributing to the WS-CAF committee, have written a useful explanation of WS-CAF in this month's issue of Web Services Journal, called Introducing WS-CAF - More than just transactions.

WS-CAF builds on the progress made by earlier standards efforts, as they illustrate with a diagram at the end of the article, showing how WS-CAF has extra layers and transaction models than either WS-Transaction and WS-Coordination (companion standards to BPEL) or BTP (a companion standard to ebXML and BPSS).

It's evident from their explanation that the effect of these extra ingredients is to extend the flexibility and adaptability of WS-CAF compared to its predecessors (or alternatives, you might call them, depending on your point of view). For example, the foundation layer of WS-CAF is WS-Context (WS-CTX). Fresh from writing my previous posting on workflow, process and pi-calculus, I couldn't help thinking that the authors' description of WS-CTX has been written by individuals with a knowing affinity for the concept of mobility:

"In general terms, a context defines basic information about the activity structure. It contains information necessary for multiple web services to be associated with the same activity, which may be dynamically updated by services as the application or process makes progress. Activities are managed by the context service, which maintains a repository of shared contexts associated with execution environments."

Further loose coupling can be achieved within the WS-CTX layer by defining separate "Activity Lifecycle Services," which add infrastructure and semantic context to individual activities on creation, thus enabling reuse (or persistence) of these contexts.

The other two layers are WS-Coordination Framework (WS-CF), which is essentially a loosely coupled superset of WS-Coordination, and WS-Transaction Management (WS-TXM), which "defines a set of pluggable transaction protocols" along with the framework for linking them into WS-CF. WS-TXM supports both ACID and long-running transactions, along with a new model called Business Process, "specifically aimed at tying heterogeneous transaction domains together into a single business- to-business transaction. For example, with the BP model it's possible to have a long-running business transaction span messaging, workflow, and traditional ACID transactions."

Those who are looking for a framework within which to combine the best of workflow, business process management and traditional transactional application architectures ought to take a long hard look at WS-CAF, and provide their constructive input to the OASIS TC.
posted by Phil Wainewright 3:36 AM (GMT) | comments | link

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