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RE: Subtyping in XML

• To: 'Aaron Skonnard' <aarons@d...>, 'Paul Prescod' <paul@p...>, xml-dev@l...
• Subject: RE: Subtyping in XML
• From: Jeff Lowery <jlowery@s...>
• Date: Wed, 4 Sep 2002 10:36:35 -0700

>> "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)
occurrence.

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

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