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Subject: Still banging on about extensibility and validation
Ken, a while back you made this interesting observation as part of a larger conversation about message validation :- >There are some who hold with a traditional view that the entire instance *has a >model*, rather than the different view that sets of labeled information found in an >instance *each have their own model*. And those sets are identified >unambiguously through the use of namespace-rich labels. >Accommodating "the entire XML instance has a model" is, I believe, more >difficult, time consuming and frustrating than accommodating "each set of >information found in an XML instance has its own model". I really want to believe this (in the practical sense of it being implementable - now) but there are a few pieces missing from my understanding which are still troubling me, perhaps you (and others) can help me out (the recent UBL SBS discussions are also surfacing some really interesting commentary). Anyway, as you had mentioned to me earlier wrt UBL code list value validation, the validation processing *must* first test that a message is compliant to the structural model (i.e. schema - maybe) before value-based validation is attempted. I think the reason was/is to confirm that the expected locations for values are present ? Also, that UBL schema do *not* use the xs:any or xs:anyAttribute wildcard mechanisms for extensibility, and in one sense UBL does not support structural extensibility by trading partners (although restriction is). This may be not entirely accurate so 'flame away'. It may also be a bit unfair of me to put this sort of question to you directly since you have already said you're really involved in the code list stuff for UBL rather than the general schema work - so apols for that :-) So, this got me thinking about how, on the one hand we want to enable trading partners to not be constrained in terms of any additional 'private' information items they may want to exchange, whilst at the same time benefit from the broader reach of standards compliance. If structural conformance is demonstrated by validating message instances to UBL schema (I mean actual XSDs - for the moment), then does that mean that :- a. there is no possibility for trading partners to 'insert' any private data into a UBL specified content model (as foreign namespaced items) even if that context make the most sense, since the message would then be schema invalid ? b. if the approach is to validate aspects of the message rather than the message as a whole, what does that mean in terms of a message that is a composite of a number of a business entity based schema, doesn't the context of where these individual parts exist in the overall message typically lend as much to validation as the individual part itself ? c. if vocabularies are best developed in a way which allows information items that are not part of its specification to be 'safely ignored' (this has been a bit of a theme that has been coming through recently), then is that really saying that traditional methods of validating messages (i.e. validating parsers which load up XSDs) won't really work, we need to move to validation via positional/context based rules (XPath) ? d. what about NVDL, (or possibly CAM and/or other methods that are being talked about). Regards Fraser.
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