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Michael Rys wrote: > > In addition, I would like to point out that in Object Data Models (including > the later releases of ODMG), there is a difference between structural type > lattices (classes in C++, aka type inheritance) and semantical collection > hierarchies (collection of objects that satisfy certain conditions that are > either necessary and sufficient or necessary, aka as class subsumption). A > common condition on such a semantical collection is, that all members are of > the same base type (the so called member type). This is exactly how you can > interpret the distinction between type (structural description) and element > (semantical role). The point in OOP is class subsumption, not structural derivation. You cannot reuse the structure without class subsumption. Why is that different in XML schema? I do not see the reason. If you are used to OOP (many people are) the XML schema specs are confusing. It is possible to add everything you want without violationg basic OOP principles, and without forcing people to learn yet another paradigm. For example, in JAVA, you have interfaces for the semantical roles without structure, but you do not need to use interfaces in your own class hierarchies if you think you do not need them. Best regards Stefan Haustein -- SAX-based access to WBXML and WML: http://www.trantor.de/wbxml XML pull parser: http://www.trantor.de/xml
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