Document misconceptions

Werner posted an article he wrote for IEEE Internet Computing titled Web Services are not Distributed Objects: Common Misconceptions about Service Oriented Architectures.

That article is very well written, and Werner makes his point loud and clear as always … but ultimately, it makes some of the same misconceptions as so many others have before it. In this case, I think I’ve boiled it down to one main misconception that I’ve talked about recently;

Web services are based on XML documents and document exchange […]

No, they are not. Just open your wallet and grab a cheque, or a credit card receipt, or your drivers license. These things are what I know a “document” to be; state. If a cop asks me for my drivers license and I hand it to her, I have performed “state transfer”, I haven’t asked her to do anything in particular by transferring this document to her. In contrast, the Web services view of a document includes a “method” which effects the semantics of the movement (aka transport) of that document. So if I had a Web services document which I handed to somebody, I’m not merely submitting that document to them, I’m asking that they perform some explicit action for me as specified by the contained method. This is a very very different thing than what “document exchange” is normally understood to mean.

I suggest that if you made the simple tweak to the big picture Web services vision to require that documents only contain state, then you’d have the Web, or at least a substantial part of it. I consider the Web to be the epitome of large scale document-centric distributed computing architectures.

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