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"Simon St.Laurent" wrote: > > XML offers computing the opportunity to behave much more like the "real > world", where communications is inexact and messy and the > standardization costs are only borne if there's a real benefit to > standardization. (ISO standardizes shipping container construction, not > which contents are appropriate to containers.) > I agree with your analogy but not, I suspect, your conclusion. We are watching a transition from "close-coupled" comms to "loosely-coupled" comms. I'm using "coupling" here to refer to how much the send and receive code has to know about the fine structure of the data being sent, from an RPC-style list of individually-typed parameters at one extreme to a single XML document at the other. This is crystalised in the web-services technology stack, and not always in the ways you might expect. SOAP, the exciting XML contender, has a spec which is focussed on close-coupled calls. The SOAP EncodingStyle allows you to serialise an RPC-style parameter set. There's nothing to stop you sending single literal XML documents, there is just no explanation of how literal XML content should be signalled, just a statement that the "section 5" SOAP EncodingStyle is the only one defined in the spec, and "There is no default encoding defined for a SOAP message." (http://www.w3.org/TR/SOAP/#_Toc478383495) WSDL makes explicit provision for both RPC-style and document-style messages - in fact for the SOAP binding, the default values for the soap:operation/@use and soap:body/@style attributes appear to make unadorned literal XML content the default. The UDDI Programmer's API 1.0, I notice, specifies that "In version 1 of the UDDI specification, the SOAP encoding feature (section 5) is not supported. Operator Sites will reject any request that arrives with a SOAP encoding attribute." We already use XML Schema structured messages to interface between major components, internal and external, of our retail finance systems. My view is that [a] single document style is far more productive than RPC style, [b] that XML Schema means that the message can use declarative validation in the comms layer rather than procedural validation in the application (and no, DTDs don't cut it for us) and [c] that XML Schemas will be the units of selection by which industry standard common message structures will evolve. Francis.
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