W3C home > Mailing lists > Public > www-rdf-logic@w3.org > April 2001

Re: Question: DAML cardinality restrictions

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 3 Apr 2001 13:36:35 -0700
Message-Id: <v0421010ab6efdd6663e5@[]>
To: David Allsopp <dallsopp@signal.dera.gov.uk>
Cc: www-rdf-logic@w3.org
>"Peter F. Patel-Schneider" wrote:
> > > Let's say I have data for a person 'A', but not for their father. Does
> > > this mean my data do not conform to the ontology/schema (since A can't
> > > point to a father instance in my small model of the world)?
> >
> > Not at all.  There is nothing in DAML+OIL that requires the data to make
> > everything explicit.  It is perfectly OK to require that people have
> > exactly one father, and also have object that belong to that class and have
> > no known specific father.
>OK. What if the data say that someone has two fathers? (for the sake of
>argument, I receive an RDF message where the person's Resource has two
>Father properties).  Presumably we must reject this message as logically

No, since it is not logically inconsistent. In fact it is not even 
legally inconsistent, given the adoption and inheritance laws.

> (Or invoke some process to decide which is the correct

If you believe that fathers are unique you can say so, and then the 
conclusion would be that these two fathers were one and the same. If 
some other source denies this (for example, if you are assuming a 
unique names regime), you have indeed found a logical contradiction. 
All of these shouldn't be built into the logic, however, as there are 
people who work by different rules in all of these cases.

>I take your point about representation, but at some point, to make
>use of our data, we will often have to leave the logical
>most software does not use FOL or anything like it, and probably never

You couldn't be more wrong.

>That's my angle - I am trying to introduce semantic web
>technology to allow _existing_ applications/agents to communicate and
>interoperate more effectively, without complete re-writes.  These
>applications, on the whole, cannot
>deal with logic, only concrete data. (If the family-tree plotting
>software can't find out _who_ Joe's father is then it isn't

Concrete data IS logic, just a narrow subset of it.

>So, I am trying to understand how I can use semantic web technology to
>allow some inference, some translation of data, some
>merging/collation/fusion of data, whilst eventually allowing me to
>extract data into more rigid forms to be imported into
>applications, displayed on screen, used to manipulate hardware, or
>Sorry to sully the pure logic with primitive unenlightened applications,
>but I can't just throw everything away and start from scratch 8-)).

You are free to do whatever you want, but there are many other kinds 
of applications. The logic doesnt prevent you from doing your thing, 
it just requires you do a little more work for yourself.

Pat Hayes

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Received on Tuesday, 3 April 2001 16:34:38 UTC

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