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ISSUE 5.6 - daml:imports as magic syntax

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Mon, 09 Sep 2002 17:23:46 -0400
Message-ID: <3D7D1162.75D74095@cse.lehigh.edu>
To: WebOnt <www-webont-wg@w3.org>

Problem: 
--------
If daml:imports is just another RDF or OWL property, then users can
place restrictions, etc. on it. For example, consider a situation where
there was a max cardinality of 1 on imports. If an ontology imported two
or more ontologies, then this would effectively say that the ontologies
are equivalent. It is probably best to avoid such situations.

Possible Solution:
------------------
This seems to indicate that imports should be a "dark" property. Note
that this isn't an issue in the Abstract Syntax, since in it, everything
is essentially "dark." In Pat Hayes' recent OWL model theory, it should
be sufficient to say that owl:imports is not an instance of owl:Object,
owl:DatatypeValue, owl:Class, owl:ObjectProperty, or
owl:DataTypeProperty. However, it would still be an rdfs:Property, but
any RDF graph that uses it as a subject or object would not be
well-formed OWL/RDF. Note, owl:imports doesn't fit into any of the
classifications in the table in section 2 of the Hayes model theory, so
perhaps a new classification called metaproperty or such is needed.

Semantics:
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It is important that the semantics of owl:imports be added to any
semantics documents. To do this, we need to be able to refer to sets of
OWL statements (such as a web page, a database with an OWL interface,
etc.) This could probably be called a resource, but that term is also
used to describe RDF instances, so for lack of a better term, I will
choose the term graph for the time being. Let graph be a function from a
URI (URL?) to an RDF/OWL graph. Each OWL graph has a set of entailments
that are determined by the model theory. The semantics of a statement:

A owl:imports B.

are:

if graph(B) |= X then graph(A) |= X

(Note: Here, "|=" is the OWL entailment relation)

One question is whether we need something more specific in the model
theory that, for example, uses ICEXT and IEXT.

Any comments or suggestions?

Jeff
Received on Monday, 9 September 2002 17:23:54 GMT

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