Derivation by Restriction
stefan.haustein at trantor.de
Sun Jan 23 12:08:56 GMT 2000
> During the writing of some C++ classes for the representation of data
> conforming with a particular schema I began to wonder about the
> "translation" of an arbitrary schema to domain specific objects
> (pretty much in the way exactml or some oracle products do nowadays
> with DTDs) and I started to wonder about the implications of
> derivation by restriction.
> What I'm looking for is whether the impedance of Der. by Rest. on OO
> apps/representations has been considered by anyone before...(not a
> basic description of how derivation works,Nikita.But thanks).
I think the main point here is that derivation in
object orientation means specialization. So if B is
a subclass of A, you can replace any occurence of A
by B. If you specialize B by restriction, that does
not hurt object orientation as long a any instance of
B is still a valid instance of A, too.
This principle would be violated if you "restrict" B
that a subelement required in A is not required in B.
In fact, that would not be a specialization or
restriction but a generalization. If I read the specs
right, you are not allowed to widen the [minOccurs...
maxOccurs] interval, so the problem you address seems
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