Re: Restriction in XML Schema

[ht@cogsci.ed.ac.uk (Henry S. Thompson)]

Jay Zhang <jz@intermicstech.com> writes:

> The definition of restriction in XML Schema reads:
> 
> >A type definition whose declarations or facets are in a
> >one-to-one relation with those of another specified type
> >definition, with each in turn restricting the possibilities
> >of the one it corresponds to, is said to be a restriction.

Note this is an introductory summary early in the spec.

> Would this definition make syntactic coincidence unduely
> significant?
> 
> Let me illustrate with an example:
> 
> Let me define a base type 'fields' as:
> 
> <complexType name='fields'>
>     <sequence>
>         <element name='field' maxOccurs='Unbound'/>
>     </sequence>
> </complexType>
> 
> would the following derived type have violated the definition
> of restriction?
> 
> <complexType name='myfields'>
>     <complexContent>
>         <restriction base='fields'>
>             <sequence>
>                 <element name='field' tag='15A'/>
>                 <element name='field' tag='20'/
>             </sequence>
>         </restriction>
>     </<complexContent>
> </complexType>

Not sure what you mean by "tag='15A'" -- this is not valid XML Schema syntax?
Leaving those out, your derivation is OK.

> However, if we define base type fields to be an equivalent:
> 
> <complexType name='fields'>
>     <sequence>
>         <element name='field' maxOccurs='Unbound'/>
>         <element name='field' minOccurs='0' maxOccurs='Unbound'/>
>     </sequence>
> </complexType>

This type violates the Unique Particle Attribution constraint, and is
not necessary for valid restriction, anyway.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
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