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RE: UFDTF Metamodeling Document

From: Conrad Bock <conrad.bock@nist.gov>
Date: Fri, 30 Nov 2007 12:44:03 -0500
To: "'Peter F. Patel-Schneider'" <pfps@research.bell-labs.com>, <ekendall@sandsoft.com>
Cc: <public-owl-wg@w3.org>, <cawelty@gmail.com>
Message-ID: <1b4d01c83378$99558570$b3200681@MEL.NIST.GOV>

Peter,

 >  > For example, graphs can span multiple documents, multiple graphs
 >  > can occur in the same document,

 >  Umm, where is the relationship between graphs and documents
 >  represented in the metamodel?  I don't see it anywhere.

I thought it was the relation between Document and RDFStatement in
Figure 10.7, but not sure.

 >  It is true that RDF Concepts does conflate statement and triple in a
 >  couple of places, but it also make the distinction clear in several
 >  other places.  RDF Semantics is quite clear that the term is triple
 >  and does not use statement in this context at all, reserving it
 >  almost exclusively for rdf:Statement.

It doesn't conflate these, as far as I can tell.  In Figure 10.2,
Statement has a property called "reified" with enumerated values for
unrefified statements (which I gather you are calling "triples"),
statements that are refified but not asserted as true, and statements
that are both refied and asserted.

 >  By the way, it appears to me that the RDF metamodel allows regular
 >  (unreified) triples (RDFStatement) to be missing a subject,
 >  predicate, or object, which is not allowed in RDF.

If your interpretation of the RDF spec is generally agreed (which
it isn't clear it is), then this would be an additional constraint on
Statement on page 40.  BTW, I notice the second paragraph above Figure
10.2 says asserted statements must have subject, object, and predicate,
but this doesn't appear in the constraints on page 40.

 >  > multiplicities (which may appear to be unintuitive to someone less
 >  > familiar with MOF as you mention),

 >  Umm, it appears to me that the metamodel states that the
 >  CommentForResource and LabelForResource relationships are 1 to many
 >  (in which direction I'm not sure).  I believe that they should both
 >  be many to many.

Just to clarify reading UML, the figure 10.3 says that RDFResource has a
property RDFScomment with cardinality zero to many, PlainLiteral a
property commentedResource with cardinality zero to one.  Whether the
place of the cardinalities is intuitive seems to depend on whether you
think in objects or relations.

 >  Agreed.  You already know my views on the best way to proceed.

Yes, just not why.  :)  Even the short alignment discussion we've been
having has turned out areas you thought were agreed among RDFers but
weren't.  Multiple structural models for OWL would severely limite
interoperability and consequencely adoption.

Conrad
Received on Friday, 30 November 2007 17:44:53 GMT

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