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RE: XML Schemas: Best Practices
- From: "Arnold, Curt" <Curt.Arnold@hyprotech.com>
- To: "'email@example.com'" <firstname.lastname@example.org>
- Date: Tue, 09 Jan 2001 10:21:15 -0700
Abstract type and type substitution does seem to work well as long as you only have one level of abstraction and only want to work on the top-level. In this case, it has some of the advantages of the
aggregation pattern that would have expressed the instance as:
<Magazine>Mag Specific Stuff</Magazine>
Generic Publication Content
Both give you some artifact in the instance that you can identify and query an element as both a Publication and a Magazine with current technologies.
Unfortunately, the type substitution approach doesn't give you a clean way of expressing in the instance a deeper hierarchy in a way that existing processors like XSLT can make meaningful queries.
Also, since the xsi:type value is a QName, unless you are restricting your document to use a fixed prefix, it would be difficult to write an XPath that would give you only the Magazine nodes.
I don't think the superclass as tag name, subclass as xsi:type pattern is generic enough to be a best practice. The aggregation pattern offers the same advantages but is more capable.