Re: Fwd: [MODS] MADS: XML schema for authorities

Butler, Mark wrote:
> RE: MADS
> 
> 
>>Converting this schema to a useful RDF is algorithmically impossible 
>>since too much information is kept implicit and/or optional.
> 
> 
> I don't think its impossible - for example of how to do it, see the enclosed
> XSLT stylesheet which demonstrates how to convert the examples. 
> 
> Writing XML in this way is quite a useful design pattern for getting
> RDF-like extensibility in XML while retaining compatibility with things like
> WSDL based web services, where we have to write an XML Schema to describe
> our data. Writing such a schema limits our ability to add extensions, so one
> way to overcome this is to use attributes to encode property names, as this
> frees us from the schema constraint. Of course once we are free of the
> schema constraint, then we lose our ability to validate, but then that's a
> problem we have with RDF as well. 

Very true.

The problem I have is not about the encoding of the semantics in the 
attributes, but the fact that those attributes are optional.

For example, in your stylesheet you write:

<xsl:template match="ref">
     <xsl:element name="{@relatedType}" 
namespace="http://web.mit.edu/simile/www/2004/06/mads-custom#">
     <rdf:Description>
       <xsl:choose>
         <xsl:when test="geographic">
           <xsl:attribute 
name="rdf:about">http://web.mit.edu/simile/www/2004/06/madsdata#<xsl:value-of 
select="str:urlencode(geographic)"/></xsl:attribute>
         </xsl:when>
         <xsl:when test="topic">
           <xsl:attribute 
name="rdf:about">http://web.mit.edu/simile/www/2004/06/madsdata#<xsl:value-of 
select="str:urlencode(topic)"/></xsl:attribute>
         </xsl:when>
       </xsl:choose>
     <xsl:apply-templates/>
     </rdf:Description>
     </xsl:element>
</xsl:template>

but in the MADS schema you get

   ...
   <xsd:attribute name="relatedType" use="optional">
   ...

so, if the attribute is not present, the XML is legal, but the 
stylesheet wouldn't work.

-- 
Stefano.