Best Practice for this problem?

[Paul Spencer <paul.spencer@boynings.co.uk>]

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

			<xsd:choice>
				<xsd:annotation>
					<xsd:documentation>At least one of Town, County and
Locality</xsd:documentation>
				</xsd:annotation>
				<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>
				<xsd:sequence>
					<xsd:element name="Town" type="bs7666:TownType"/>
					<xsd:element name="Locality" type="bs7666:LocalityType"/>
				</xsd:sequence>
				<xsd:sequence>
					<xsd:element name="Town" type="bs7666:TownType"/>
					<xsd:element name="County" type="bs7666:CountyType"/>
				</xsd:sequence>
				<xsd:sequence>
					<xsd:element name="Locality" type="bs7666:LocalityType"/>
					<xsd:element name="County" type="bs7666:CountyType"/>
				</xsd:sequence>
				<xsd:sequence>
					<xsd:element name="Town" type="bs7666:TownType"/>
					<xsd:element name="Locality" type="bs7666:LocalityType"/>
					<xsd:element name="County" type="bs7666:CountyType"/>
				</xsd:sequence>
			</xsd:choice>

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

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.

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.

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?

Any thoughts?

Regards

Paul Spencer