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comments on DAML-ONT semantics document

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 14 Nov 2000 14:23:44 -0500
To: www-rdf-logic@w3.org
Message-Id: <20001114142344K.pfps@research.bell-labs.com>
Comments on 
	 An Axiomatic Semantics for DAML-ONT
	 (version of November 13, 2000)

I have a number of questions concerning An Axiomatic Semantics for DAML-ONT
(version of November 13, 2000).  Let me start with what I consider the most

I don't see how this document is much help in determining the semantics of
DAML-ONT.  The document translates DAML-ONT into axioms written in KIF.
This might be helpful if the axioms were regular first-order axioms,
but they instead use many constructs that, to me, are just not natural. 

For example, the document heavily uses the predicates ``holds'' and
``type'', which, I suppose are supposed to mean that a relation holds
between two objects or an object belongs to a category, respectively.
However, neither of these are defined in the document.  Further, although
``holds'' is mentioned in the KIF standards document, it is not given any
definition therein, nor it is given a semantics in the model theoretic
semantics for KIF.  ``type'' is not even mentioned in the KIF
documentation.  It is fairly obvious what the intended meaning of these two
predicates are, but this intended meaning is a second-order one, and this
need for a second-order semantics doesn't seem natural at all to me.

In addition, and perhaps even more importantly, as these two predicates are
vital to the semantics there is no way that this document can provide a
semantics for DAML constructs.

There are quite a number of other errors in the document:
1/ ``Disjoint'' is supposed to be a class, but it is certainly not in the same
   category as ``Thing'' or ``Person''.
2/ There is no way that ``domain'' relationships can be inferred.  The only
   definition of ``domain'' is given in Ax92, and this is a one-way axiom.
3/ There is no way to infer that ``Thing'' and ``Nothing'' are in the
   ``ComplementOf'' relationship as ``Thing'' and ``Nothing'' have direct
   definitions, but ``ComplementOf'' is defined in terms of ``holds''.
4/ ``oneOf'' is defined to belong to ``Property'', but it looks more like a
5/ ``asClass'' is defined as equality.  This means that two classes related
   by ``asClass'' are the same object, which is not what is meant by
   equivalency in most KR systems.  
6/ There is no way of getting from a knowledge base to a ``values-list''.
7/ ``values-list'' has two arguments in some places and three in others.

There are also a number of things that look like errors:

1/ ``Thing'' and ``Nothing'' are given meaning without referring to
   ``holds''.  These are the only two classes that are given meaning in
   this way.
2/ There are lots of things that belong to ``Property'', which I assume has
   some relationship to RDF properties, but there is no such connection.
3/ There is no inclusion of any RDF stuff.  For example, I expected to see
   a mapping of RDF constructs into KIF, or at least a reference to such.
   Things like ``Seq'' thus are not defined.
4/ There is no meaning provided for ``Default''.

There are other things that are just plain ugly:
1/ The ``values-list'' mechanism depends on a lot of ugly machinery.

I'm sure that I am missing more problems.

Peter F. Patel-Schneider
Received on Tuesday, 14 November 2000 14:24:02 UTC

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