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   Schema Question: Derived Types

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  • From: Michael Anderson <michael@research.canon.com.au>
  • To: xml <xml-dev@xml.org>
  • Date: Fri, 10 Mar 2000 09:20:51 +1100


Why do we have to restrict a type derivation to either an "extension" or
a "restriction" - let's forget for the moment about "reproduction" and
"list".  Such restriction, at times, makes it necessary to define some
dummy type as an intermediate step in order to define a sub-type that is
both an extension and restriction to a type.  I think it is rather
common, say, for a sub-type to extend a type's content model and add new
attributes while, at the same time, restrict the values and cadinality
of some other attributes.

Could extension and restriction be achieved at the same time by tagging
part of a type definition as restriction and the other part as
extension?  For instance,

<complexType name="B" base="A">
                <attribute name="attr1" fixed="some fixed value" />
                <attribute name="attr2" minOccurs="1" />
                <element ref="newElement" />
                <attribute name="attr3" type="string" minOccurs="1" />


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