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Re: UFDTF Metamodeling Document

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 30 Nov 2007 08:57:08 -0500 (EST)
Message-Id: <20071130.085708.75510493.pfps@research.bell-labs.com>
To: ekendall@sandsoft.com
Cc: public-owl-wg@w3.org, cawelty@gmail.com

From: "Elisa F. Kendall" <ekendall@sandsoft.com>
Subject: Re: UFDTF Metamodeling Document
Date: Fri, 30 Nov 2007 05:37:18 -0800

> The RDF metamodel in particular was reviewed extensively by HP Labs, Pat 
> Hayes, numerous IBM Watson folks, other OMGers who are metamodeling 
> experts or have implemented RDF-based applications, and while I will go 
> back to them with your comments, below, to verify the metamodels and 
> related text again, I believe the RDF metamodel chapter of the ODM 
> specification is correct with respect to most, if not all of your 
> comments, below.
> 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.

> the relationship between statements 
> (triples) and graphs in particular was reviewed extensively and was the 
> subject of significant debate for several weeks.  The RDF documents are 
> unclear about a number of the issues you've raised, thus we worked with 
> the RDF community, and in particular HP Labs, to ensure that the ODM was 
> correct and as unambiguous as possible.  The same is true for the 
> reification language and approach, use of the word statement rather than 
> triple (which we also debated at length, and which Pat and Chris Welty 
> assisted us with may be a matter of taste -- it is used interchangeably 
> in many places in the RDF documents), 

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.

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.

> 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.

> optional naming of graphs (per SPARQL), 

How did SPARQL get into a metamodel for RDF?

> and so forth.

> One option with regard to OWL would be to provide extensions to the 
> current OWL metamodel for those who depend on RDF, corrections where 
> required, and, maybe -- I can't commit to this without discussion in the 
> OMG community -- an additional OWL DL only metamodel, divorced from the 
> RDF metamodel, for those, such as some members of this working group, 
> who need the standalone approach for some of the applications that Boris 
> named.  This could be done in a revision to ODM, once the language 
> developed by this community is sufficiently stable, and in a way that 
> would clearly provide conformance requirements to users, the 
> relationship between the two metamodels, and so forth.  Having said 
> this, I stand by my comment that we need to be thoughtful about what we 
> would do here to limit confusion among those in the community who have 
> already implemented, are in the process of implementing, or may 
> implement tools that use the specifications.  

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

> This community is, in 
> fact, significantly larger than you might imagine -- which we learned 
> only from statistics on downloads of presentations, etc.  One 
> presentation given early this year in particular was downloaded over 
> 2000 times within a few short weeks.
> Thanks,
> Elisa

Received on Friday, 30 November 2007 14:13:51 UTC

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