Re: extension vs restriction

richard torres <richard.torres@yale.edu> writes:

> I understand how extension works, but am confused about restriction.  Do
> you have to repeat everything that is not changed.

> With restriction
> type 1
>     element 1 minOccurs=0 maxOccurs=1
>     element 2 minOccurs=0 maxOccurs=1
>     element 3 minOccurs=0 maxOccurs=1
> 
> Which is correct to delete element 1, but keep 2 and 3 as they are?
> 
> type 2 by restriction of type 1
>      element 1 maxOccurs=0
> 
> or
> 
> type 2 by restriction of type 1
>     element 1 maxOccurs=0
>     element 2 minOccurs=0 maxOccurs=1
>     element 3 minOccurs=0 maxOccurs=1

The second is correct, but not minimal.  To define by restriction, you
provide a complete content model, which must be matchable one-to-one
back to the old one.  So in the case above you can say:

 type 2 by restriction of type 1
     element 2 minOccurs=0 maxOccurs=1
     element 3 minOccurs=0 maxOccurs=1

Things can be left out as long as they were optional in the base.

For attributes, since there's no ordering to help with the matching
up, you _must_ use the maxOccurs=0 approach, and things not mentioned
are copied.

ht
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  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
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