code list validation

["Ray Denenberg, Library of Congress" <rden@loc.gov>]

One of our interests at the Library of Congress  is to be able to point to
an external codelist, rather than include it within an XML schema. (I'm not
talking about validating, which I accept is out-of-scope.)

In other words, instead of saying:

<xsd:restriction base="xsd:string">
<xsd:enumeration value="1"/>
<xsd:enumeration value="2"/>
<xsd:enumeration value="3"/>
<xsd:enumeration value="4"/>
<xsd:enumeration value="5"/>
<xsd:enumeration value="6"/>
<xsd:enumeration value="7"/>
</xsd:restriction>

You could say:
<xsd:restriction base="xsd:string" codelist="http://....."/>

There is no such syntax yet (that I'm aware of), most likely because there
is no standard codelist format yet. But it might be as simple as above -- 
defining a 'codelist' attribute on the restriction element within the schema
language. Of course it would need to be accepted into the language by the
W3C.

(I know there are suggested approaches using 'import' and 'include' but
these are too sloppy. We currently use comments or annotations to point to
external lists. But when we have a standard format for a codelist, and if
there is syntax to point to it, people will begin to develop validation
software.)

I think this would have significant utility, and it seems so simple. Would
it be reasonable for this TC to formulate a recommendation along these
lines, and forward it to the W3C?

--Ray Denenberg, Library of Congress