Re: existential answers to queries

From: Ian Horrocks (
Date: 10/25/01

On October 25, Richard Fikes writes:
> > As I said in my other messages, I believe that
> > returning "skolems" could have many/serious consequences for the
> > decidability, tractability etc. of the query language. Infinite
> > answers is just one of these that springs to mind.
> Without adding any comments to the "skolems" issue, I would like to
> point out that I think we must deal with queries that have potentially
> infinite answers.  In particular, since the XML data types are now part
> of DAML+OIL, we have classes with an infinite number of instances,
> namely the class of integers.  So, the query is "RDF(type ?x Integer)"
> will have an infinite number of answers.  

OK - but given the structure of the language and the strict separation
of datatypes from "object" types, it should be pretty easy to deal
with this kind of thing (actually, how to deal with datatypes in
queries/answers could be treated as a separate issue).  This
definitely isn't the case for queries that could return an infinite
number of "skolem" individuals/tuples - it may not even be possible to
detect this situation.


> Richard

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