Re: Restriction in XML Schema

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

"Jay Zhang" <jz@intermicstech.com> writes:

> Restriction is a very important construct. I need to have a clear
> understanding of its definition. There is the distance between elegant
> semantic definition and computation-oriented syntactic definition.
> 
> My sloppy example clouded my question the first time. (Who
> does not have a personal abbreviation of such a verbose language?;-)
> 
> Let me try again.
> 
> The base type is defined as:
> 
> <complexType name='fields'>
>   <sequence>
>     <element name='field' maxOccurs='2'>
> 
>       <complexType>
> 
>         <attribute name='tag'/>
> 
>       </complexType>
>     </element>
> 
>   </sequence>
> </complexType>
> 
> Let me derive the following type:
> 
> <complexType name='myfields'>
>   <complexContent>
>     <restriction base='fields'>
>       <sequence>
>         <element name='field'>
>           <complexType>
> 
>             <attribute name='tag' use='fixed' value='15A'/>
> 
>           </complexType>
> 
>         </element>
> 
>         <element name='field'>
>           <complexType>
> 
>             <attribute name='tag' use='fixed' value='20'/>
> 
>           </complexType>
> 
>         </element>
> 
>       </sequence>
>     </restriction>
>   </<complexContent>
> </complexType>

Nope, sorry.  You now have a single element ('field') with two
different types in the same content model.  We decided in the
interests of preserving some obvious processing invariants that that
would not be allowed.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/