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> b) Definitely the underlying schema model should be extremely generic and > independent of any concrete syntax. The lack of such a model in > XSD is very > disturbing. Perhaps this is the crux of people's objections to > putting vital > semantics into schemas. XSD isn't tied to its transfer syntax. In fact, there may be cases where XSD components can not be represented by the transfer syntax, although I know of none. Also, for those mathemeticians out there, MSL provides a normative mathematical model of XSD. So I'm not sure exactly what your complaint is. > Equally disturbing is the lack of a decoupled > extensibility mechanism like Tibco's Schema Adjunct Framework. > Sure we have > "appinfo", but embedding this metadata directly in the schema is > another big > problem because the schema has to be modified for each > application that uses > its own types of semantics. How would you associate an adjunct with a schema without editing the schema? Also, what is wrong with modifying a schema with application semantics? I know the systems I work with will not be retrieving remote copies of schema to do validation because of availability and trust issues. They will use local copies. > The underlying semantics will always be the > same, but a database application clearly needs different metadata from a > Bean generator. The fact there isn't a built-in mechanism for associating > multiple files containing schema-level metadata with a schema is a big > mistake responsible for much of the bloat in the spec. Would this kind of > approach alleviate people's objections to using schemas as the underlying > model for XML-based software architectures? I disagree that the bloat in schema is due to this. First, XSD supports generating a schema based on multiple schemas. Second, XSD validation rules support validating an instance against multiple schemas that may have no connection with each other whatsoever. Can you give an example of the kind of metadata that is narowly focused and causes bloat in the spec? David Cleary Progress Software
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