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Re: Restriction in XML Schema

  • From: ht@c... (Henry S. Thompson)
  • To: Jay Zhang <jz@i...>
  • Date: Mon, 05 Mar 2001 13:22:05 +0000

maxoccurs unbound
Jay Zhang <jz@i...> 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
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@c...
		     URL: http://www.ltg.ed.ac.uk/~ht/

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