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Re: Making Rules Out of RDF-Graphs (Re: What is an RDF Query?)

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 17 Sep 2001 19:01:28 -0400
Message-Id: <200109172301.f8HN1Ss03097@wadimousa.hawke.org>
To: Pat Hayes <phayes@ai.uwf.edu>
cc: www-rdf-rules@w3.org

> >You might well Skolemize it like that internally (you'd have to if you
> >were giving it to a Horn logic engine), but if you require users to do
> >it, then the rule-conclusion language needs to have functions in it.
> >I'm suggesting that we try making RDF rules out of less-expressive
> >stuff (to use the technical term) than that.
> 
> Why? (Not that there might not be valid reasons, but I wonder what
> yours are. )
> 
> I think there has been too much emphasis on sticking to very 
> inexpressive languages. More expressive languages are often *easier* 
> for users (though admittedly not for inference engines; but I really 
> do not think that the kinds of ontologies we are going to see on the 
> semantic web in the near future are going to tax the resources of a 
> modern inference engine for full FOL, to be honest.)

One of my main reasons may be a fantasy of this stuff being used for
real distributed programming, where code is moving around, and having
that code be declarative (eg pure prolog instead of java byte code).
That's kind of off-topic here, though.

Here, ... I dunno.   I guess ease of implementation is actually
important.  I think techies who have never really done much with logic
system will have an easier time thinking about Horn logic.   

I suppose there's a very important question in how the different
logics might play together.   Tim B-L seems to have a vision for this
which I don't understand.

> Well, RDF is too fixed to alter in this way now, but RDF+ could allow 
> this extension with really minimal change either to the syntax or the 
> inference engines that are being built. Once you have a run-time 
> variable binder and some kind of search engine that can switch 
> bindings between paths, adding functional terms is just a matter of 
> extending the binding code to be recursive. Prolog hackers have some 
> blindingly fast unifiers which do this very effectively.

Yeah, I just don't know anything about the path to "RDF+".

     -- sandro
Received on Monday, 17 September 2001 19:05:25 GMT

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