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Re: Graph-to-Graph Inference Rules (GGIR)

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 10 Oct 2001 15:51:21 -0500
Message-Id: <p05101049b7ea63b74534@[205.160.76.193]>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-rules@w3.org
>  > >
>>  >    I think with this kind of approach, the interpretation of bNodes as
>>  >    file-scope existential variables works perfectly.  In the premise,
>>  >    they are just anonymous universal variables (because they are inside
>>  >    the "if"), and in the conclusion they become skolem functions of the
>>  >    universal variables, which is very useful.
>>  >
>>  >I think you pulled a fast one there.
>>
>>  Not if you interpret 'premis' and 'conclusion' as applying to an
>>  inference rule (or sequent) rather than an implication. I think that
>>  is what Sandro had in mind (yes?)
>
>Yes.
>
>>  >If the variables are really
>>  >file-scope existentials, then a rule would look like this:
>>  >
>>  >ex x ((P x) -> (Q x)) 
>>  >   [the 'ex x' might actually be way outside the implication,
>>  >    which is just one of many things in the file]
>>  >
>>  >This is not equivalent to
>>  >
>>  >ex x ((fa x (P x)) -> (Q x))
>>  >
>>  >or to
>>  >
>>  >fa x ((P x) -> (Q x))
>>
>>  But think of the rule instead as a relation between two RDF graphs
>>  that indicates an extra-logical entailment licence, and allows one
>>  graph to be transformed into another. Then the claim makes sense,
>>  since none of the *logical* scopes go across the arrow (which really
>>  ought be written |- rather than -> )
>
>Yeah.  
>
>So, is this list (rdf-rules) the place to talk about inference rules
>like this, and www-rdf-logic the place to be if you want to talk about
>logical implication (with generalized modus ponens, or resolution, or
>something as your inference rule).....?  That is, is the focus of
>www-rdf-rules extra-logical (in the sense Pat means)?

People differ on that question. If we were all using GOFFOL, then the 
question wouldn't matter much since there are obvious mappings 
between them. As some of us are committed to less expressive 
languages, however, for one reason or another, we have to be more 
careful to make distinctions. As to which list is appropriate, I can 
no longer clearly distinguish these various rdf-??? lists apart.

>I imagine using a set of these rules as a kind of filter, a stage in
>a pipeline of processing an RDF Graph.
>
>What I can't figure out is whether or when it's better to use these
>Graph->Graph Inference Rules and when it's better to just use logical
>implication.

Some folk think that talking about rules is more general than talking 
about implication, since there can be rules even for logics that 
don't have implication (such as RDF, say ;-)
I'm not sure what you mean by 'just using' logical implication 
though. Logical implication by itself doesn't actually DO anything, 
it just sits there and either is or isn't true.

>On the surface, GGIR looks faster, but less flexible,
>and not naturally transmitted along with the data.  It's more like a
>program that processes data (and via Prolog becomes one).
>
>But this seems like a false dichotomy when I look deeper, since an
>agent can fairly easily map back and for between the two (in at least
>the areas where the expressiveness is the same).

Right, if the agent has the smarts and the authority to use an 
expressive enough language, at any rate.

Pat Hayes
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Received on Wednesday, 10 October 2001 16:51:30 GMT

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