Karen Coyle wrote:
>
> The above looks really odd to me -- I'm not at all sure that you can 
> use the class Agent in that way.... I was of the impression that 
> classes are used in metadata definitions, but not in instances. Am I 
> wrong?

I'll answer my own question: yes, I'm wrong. Here's an example from the 
RDF primer:

<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
            xmlns:ex="http://example.org/schemas/vehicles#"
            xml:base="http://example.org/things">

  <ex:PassengerVehicle rdf:ID="johnSmithsCar">
       <ex:registeredTo rdf:resource="http://www.example.org/staffid/85740"/>
       <ex:rearSeatLegRoom 
           rdf:datatype="&xsd;integer">127</ex:rearSeatLegRoom>
       <ex:primaryDriver rdf:resource="http://www.example.org/staffid/85740"/>
  </ex:PassengerVehicle>
</rdf:RDF>


So <frbr:Work> and <frbr:Expression> also appear to work as classes, if 
that's what you intend. I still can't wrap my head around what they are 
*functionally.* As far as I can tell, classes give you categories, but 
don't themselves have properties, so they don't function like the class 
in OOP. At best, it seems that you get:

A is of class X
B is of class X
C is of class X
therefore: class X = A, B, C

But if someone else states that
B is of class Y

then my question is: has B changed? In other words, is B of class X the 
same as B of class Y? (Assuming that both B's have the same URI.). Again 
this seems to get back to flexible v. specific. The more flexible you 
want to be, the more you depend on context. The more specific you are, 
the more your metadata is independent of context. So for me it comes 
down to functionality, which is how much context do I want to carry 
around in order to make sense of my metadata? I think for the purposes 
of open data exchange, context adds overhead.

kc

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Karen Coyle / Digital Library Consultant
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