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Comments on RDF: Concepts and Abstract Data Model

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 06 Sep 2002 20:51:22 -0400 (EDT)
Message-Id: <20020906.205122.58014113.pfps@research.bell-labs.com>
To: www-rdf-comments@w3.org

Some Comments on

   Resource Description Framework (RDF):
   Concepts and Abstract Data Model

The title of Section 2.2.6 is misleading at best, and just plain wrong
at worst.  RDF cannot ``say anything about anything.''  For example,
it cannot say that every person has at most one parent.  So what can
RDF say?  Does RDF allow ``universal expression of ground facts'', as
stated in Section 2.2.7?  No, RDF cannot say, for example, that Sue or
Ellen is John's sister, or that Sue is not John's sister, or that if
Sue is John's sister then so is Ellen, all of which are ground facts.
Maybe RDF can say atomic ground facts?  No, RDF cannot say, for
example that there is an purchase property between John, Susan, and
John's pet rock.  Is there any place in the document that correctly
states what RDF can say?  Not that I could find, not even the
statement that RDF can say ``assertions of specific properties about
specific named things'' because that ignores unnamed (or blank) nodes
in RDF graphs.

The document says that to support use by automated tools ``certain
meanings of RDF statements must be defined in a very precise
manner''.  Does this mean that there are several, possibly different,
meanings of RDF statements?

The document says that the RDF core language has ``no machinery for
formalizing allowable inferences''.  What then is RDF closure as defined in
the RDF Model Theory document?

The documents says that many of the nodes in an RDF graph are blank
and some are labelled.  Why the differences?  Does this mean that
there can be no RDF graphs where all nodes are labelled?  

Peter F. Patel-Schneider
Bell Labs Research
Received on Friday, 6 September 2002 20:51:30 UTC

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