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A missing piece

For some time now I have been thinking that the key to a framework for safe and effective action across the Internet was the Norms and Institutions paradigm. In that paradigm, the key concept (it seems to me) was the social act; or rather, that all human actions are rooted in the social context.

At the same time, we have been working on the SOA Reference Architecture, and I feel that it is important that SOA itself be grounded in the N&I paradigm. In the approach that we are taking, we are taking multiple views on the SOA theme. Each view is characterized by a viewpoint -- literally a point of view of the architecture. One of these views is the Service as Business view, and this view is expressed in language that would be instantly familiar to anyone aware of the Norms and Institutions framework.

A challenge in such a multi-layered approach to architecture is to link the different levels together in a convincing way (ideally, in a way that is both clear and obviously supporting).

In this case, one such challenge is in linking the information exchange level of the SOA (e.g., SOAP message exchange) with the business view (e.g., buying a book). It is certainly true that any interpretation of a SOAP message as anything other than a bunch of XML is somehow extraneous to the SOAP message itself. SOAP (and related specs) simply does not have the language or conceptual framework to deal with book buying (say).

Hence the concept of a business transaction. For business types, this is a fundamental idea: we agree that you will ship me the book and I will pay for it. From the business perspective how this agreement is reached is pure IT (and boring).

For us, however, we need to relate a business transaction to an interchange of SOAP. This leads to the concept of supervenience.

One system can be said to supervene over another if (a) the first system uses the second in a replaceable manner (a different message exchange mechanism would do just as well) and (b) the second lower-level system is neutral in respect of the higher-level system. I.e., if the higher-level use is simply one possible application of the lower-level system and could be applied to other uses without fundamentally affecting its functioning.

So, the business transaction 'system' supervenes on the message exchange system quite nicely. Another way of saying this is that business transactions provide an effective way of capturing the meaning of SOAP-level information exchange at a level that is meaningful to people who are not IT geeks.

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