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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Personal reply to Edd Dumbill's XML Hack Article wrt W3C XML Schema
 Matthew Gertner wrote: > I can't see any scenario where semantics as fundamental as data types would > vary for a given XML element type across > instances. > > Element types have specific semantics that don't very across instances. I > would have thought that this would be one of the few universally accepted > truths in the XML world (wishful thinking, I guess). Specifying data types in > the instance for convenience runs directly counter to this. Without diminishing any of the points which Eric makes in his reply, let me address this one point directly. I am learning that my daily experience over nearly twenty years of what data is and how it is processed is strikingly different from what you and so many others are apparently accustomed to. In my daily experience 'semantics as fundamental as data types' vary for a given XML element [I cannot say, as you did, 'element type', because that begs this very question], not only across instances but across different uses of the same instance. I take orders for transactions in securities, generated in accordance with the business practices, regulatory constraints, and portfolio strategies in one environment and transmit them for execution to another, entirely different environment. For the purposes of the processing which is performed with expertise unique to that receiving environment, what had been a numeric (of whatever specific type) in the transmitted order document may well be instantiated as a boolean value, or as a string for processing as text in the presentational output of a hardcopy record of the transaction, which might be the only use for a particular element in that processing environment. Once the order is executed, a new record documenting that transaction is transmitted, along with the original order document, to a number of interested parties. Those parties have different functions and therefore widely differing data needs, and therefore different uses for and understandings of the elements in each of these two documents. If the receiver of these two documents performs cashiering in the UK, it will perform different processes, which elaborate very different semantics from individual elements of the document instance, than will a receiver performing regulatory compliance reporting in the US. Both recipients have equal standing as interested parties to those two documents; neither of them is the primary user, so that the other's uses for and understanding of the data are somehow secondary. Likewise, the data understanding of one is is no way derived from or dependent on that of the other, nor are they both somehow secondary or subordinate in their understanding of the data because their use of it follows that of the first user who executed the initial transaction. The point here is that no party--not the sender, and none of the downstream receivers--has the standing to fix the semantics of the elements transmitted in the XML document. Notice also that I am not talking about 'specifying datatypes in the instance'. The data types and their semantics are as elaborated in the processing performed upon the instance, which may vary in each case. 
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