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Re: Best Practice for this problem?

Paul Spencer <paul.spencer@boynings.co.uk> writes:

> I have recently been asked to look at a schema, of which this is a part:


> The intention is clear - at least one of the three elements <Town>,
> <Locality>, <County>, but each must not appear more than once.

There are several problems here -- first of all, you are breaking the
unique attribution rule.  Second of all, you haven't got all the bases 

The DTD equivalent of what you want is

Just transcribe this into XML Schema.

> I believe the format to be non-compliant with XML Schema since each of the
> three elements has multiple definitions within the same scope. XML Authority
> 2.1 agrees with me, XML Spy 3.5 does not.

Nope, they all have the same type, so that's OK.

> If I am right, there are two choices:
> 1. Define the three elements globally, then reference them as required. This
> loses the benefit of a local definition within the complex data type.

You could certainly do that.

> 2. Define the elements as at the start of the example:
> 				<xsd:choice>
> 					<xsd:element name="Town" type="bs7666:TownType"/>
> 					<xsd:element name="Locality" type="bs7666:LocalityType"/>
> 					<xsd:element name="County" type="bs7666:CountyType"/>
> 				</xsd:choice>
> Then access by reference from there. For example:
> 				<xsd:sequence>
> 					<xsd:element ref="Town"/>
> 					<xsd:element ref="Locality"/>
> 				</xsd:sequence>
> I have never seen an example that uses "ref=" pointing to a locally scoped
> definition. Is this allowed?

Not allowed, although we considered it and may come back to it.

  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/