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on owl:imports

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Thu, 14 Jun 2007 16:03:31 +0100
Message-ID: <467158C3.6000404@hpl.hp.com>
To: Alan Ruttenberg <alanruttenberg@gmail.com>, Owl Dev <public-owl-dev@w3.org>


Hi Alan

following up from our chat yesterday, (but note public list), you 
mentioned how some of the possible constructs in OWL Full seemed totally 
useless and just plain confusing.

Two you mentioned were:

what would

rdf:type rdf:type rdfs:Class .

mean?

And what would:

restriction( owl:imports, minCardinality(4) )

mean?

The general OWL Full mentality, is to allow people to say things, 
including unhelpful things, and then to take a garbage-in garbage-out 
type approach.

For instance, earlier today I have been answering a question on the jena 
support list concerning an intersection of a class and a datatype 
property: unsurprisingly not what was intended.

But, it has occurred to me that the restriction on owl:imports is, in 
fact, plausibly useful in some cases.

Here goes:

I have been investigating improving Jena's performance.
A possible area of investigation is how well does Jena perform when a 
large number of imports have been made.
As long as each ontology is a semantically distinct thing then

restriction( owl:imports, minCardinality(4) )

is the class of ontologies that have imported at least 4 ontologies.

This may be a useful class of ontologies to concentrate my performance 
tests on.

To make that work within a reasoner, I would have to augment the formal 
OWL Semantics, perhaps, to make

uri1 rdf:type owl:Ontology
uri2 rdf:type owl:Ontology
uri1 owl:sameAs uri2

into a contradiction (when uri1 and uri2 differ). This would reflect 
some sense of the meaning of the uri of an ontology being its (unique?) 
name. I believe that would be a compliant extension to the semantics 
(although not one that I would propose for standardization).

Probably to answer the most useful question in this case I would want a 
transitive superproperty of owl:imports, and then ask the minCardinality 
question: this would give me a class of ontologies whose import closure 
is large.

=====

I am not trying to claim that this is an important use case, that must 
be addressed - I am more trying to articulate a mentality: we have a 
powerful tool for describing resources on the web and their 
relationships - it can be used to help with a number of tasks.

The limitations of OWL DL guarantee certain computational properties, 
but at the cost of syntactically prohibiting certain constructs, most of 
which do not address the main tasks of traditional ontologies.

It doesn't mean that such constructs are useless.


Jeremy





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Received on Thursday, 14 June 2007 15:04:08 GMT

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