On 1 Feb, 07:49, Pavel Lepin <p.le...@ctncorp.com> wrote:
> mnicke...@gmail.com <mnicke...@gmail.com> wrote in
> <f0461272-9799-42a5-a909-1673f4256...@d70g2000hsb.googlegroups.com>:
>
> > I'm still learning, so apologies if this is trivial...
>
> ...
>
> > <Record>
> > =A0 =A0<foo id=3D"a">... </foo>
> > =A0 =A0<foo id=3D"b">....</foo>
> > =A0 =A0<foo id=3D"c">.....</foo>
> > </Record>
>
> > Is it possible to create an xsd file that enforces that
> > within the <Record> block there exists exactly three foo
> > tags each containing a different id value (from the enum
> > a, b, and c )?
>
> It is possible.
>
=2E..
> =A0 <xs:element name=3D"foo">
> =A0 =A0 <xs:complexType>
> =A0 =A0 =A0 <xs:simpleContent>
> =A0 =A0 =A0 =A0 <xs:extension base=3D"xs:string">
> =A0 =A0 =A0 =A0 =A0 <xs:attribute ref=3D"id" use=3D"required"/>
> =A0 =A0 =A0 =A0 </xs:extension>
> =A0 =A0 =A0 </xs:simpleContent>
> =A0 =A0 </xs:complexType>
> =A0 </xs:element>
> =A0 <xs:attribute name=3D"id">
> =A0 =A0 <xs:simpleType>
> =A0 =A0 =A0 <xs:restriction base=3D"xs:string">
> =A0 =A0 =A0 =A0 <xs:pattern value=3D"(a|b|c)"/>
> =A0 =A0 =A0 </xs:restriction>
> =A0 =A0 </xs:simpleType>
> =A0 </xs:attribute>
> </xs:schema>
> ...

I don't know what other peoples' opinions are, but in general I think
I would avoid doing a ref to an attribute.  My reasoninig is that in
XML documents attributes are generally unqualified (although there are
numerous exceptions to this such as xml:lang etc.).  If an XML
namespace is present, then globally defined attributes are namespace
qualified.  Agreed, this schema does not define a targetNamespace, so
the issue doesn't arise; at the moment.

However, if as the schema is evolved it's decided to give it a target
namespace, then the attribute will become qualified.  This could
potentially make it difficult to migrate any existing XML instances.
For example, as we all know, a simple way to make an XML instance
namespace qualified is to use the default namespace (xmlns=3D"foo"), and
that could potentially be a simple localized fix.  But unqualified
attributes always belong to no namespace, so this wouldn't fix the
attributes, and a more detailed fix-up would be required.

Just my thought - and I'd interested to hear others!

Pete Cordell
Codalogic
Visit http://www.codalogic.com/lmx/ for XML C++ data binding