Entities and namespaces in XSchemata
This is probably blindingly obvious to everyone already (especially SGML experts) but I had a sudden revelation today. Essentially everything that parameter entities do in ordinary DTDs maps onto general or text entities in XSchemata. Thus by crafting your XSchemata in XML you get - for free - the maintainability produced by entities: <!DOCTYPE XSchema SYSTEM "xschema.dtd" [ <!ENTITY bar.default "plugh"> ]> <ElementType id="foo"> <Attribute id="bar"> <Type>CDATA</Type> <Default>&bar.default;</Default> </Attribute> </ElementType> I am not an XML/SGML theorist, but it seems to me that anything that PEs can do for DTDs can be mirrored by entities in XSchemata. This extends to content specs, and - this could be exciting - namespaces. Watch: <!DOCTYPE XSchema SYSTEM "xschema.dtd" [ <!ENTITY cml "CML:"> ]> <ElementType id="&cml:mol"> <ContentSpec> <Seq optional="no" repeatable="no"> <ElementType>&cml;atoms</ElementType> </Seq> <Seq optional="yes" repeatable="no"> <ElementType>&cml;bonds</ElementType> </Seq> </ContentSpec> </ElementType> To me this looks as if we can create our DTDs to be namespace-aware and - if necessary - reconfigure them. Thus if I have to change the prefix CML because of a clash with the Caledonian Music Lovers, I simply have to edit one ENTITY in the XSchema. [If there is an sgmls-like 'include' facility in the software, then I can even do it at runtime.] Since we have committed to reconstituting 'normalised DTDs' from XSchemata, doesn't this take us forward in maintaining namespace-aware DTDs? (We can't do it in conventional ones, because PEs don't apply to elementTypes). P. Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic net connection VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary http://www.venus.co.uk/vhg xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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