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   RE: [xml-dev] Subtyping in XML

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>> "Extending"
> > a document type can break applications which is more or less what
> > happens in binary formats too!
> Type inheritance in XML Schema can provide extensibility 
> benefits to the
> author of the original schema. 

The gist of the argument is that in OOP, one cannot change the cardinality
of a mutator function.  In other words, I can't change addFoo() to
addFoos(), or put tack an additional addFoo() function onto a base type
through extension. In XML Schema you can, in essence, violate the
cardinality restrictions of an element of a base type, so long as the new
elements are distinct _in position_ from the original (constrained)

So how would you model such a datatype extension in an OOP language?  Not
naturally, that's for sure.


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