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Re: What is an RDF Query?

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 11 Sep 2001 13:47:49 -0500
Message-Id: <v04210103b7c40b5507d9@[]>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-rules@w3.org
> > >I agree that RDF queries and RDF rule premises
> >
> > Er.....actually, rule consequents/conclusions are more like queries
> > than rule premises are. Is that what you meant?
>Um, no.
>Here's a rule:  If Ralph is in his office, then Ralph is at MIT.
>                    \                  /         \           /
>                     \                /           \         /
>                          Premise                 Conclusion
>                        (Antecedent)             (Consequent)
>We could make either part into a query:
>       Is Ralph in his office?

There is no way to answer that, given this rule. The rule simply 
doesn't connect to this query in any way.

>       Is Ralph at MIT?

He is if he is in his office, otherwise you don't know (from the rule)

>But it seems much more natural to think of the premise as a query; it
>leads us to a very simple algorithm:
>      query: Is Ralph in his office?
>      on success: we can conclude Ralph is at MIT.
>      on failure: we can't conclude anything from this.

You are here applying the rule to draw a conclusion.  But it is 
invalid to draw a conclusion from a query. Querying is like asking 
whether something is true, ie whether it *follows from* what has been 
asserted by the sources you trust. Rules allow you to conclude 
conclusions, but they don't allow you conclude their antecendents.

>How else do you see it?

See any logic textbook, Sorry , but this is really very basic stuff.

Pat Hayes

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Received on Tuesday, 11 September 2001 12:46:30 UTC

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