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Re: RIF-in-RDF: Requirement 4 [Switching to KR Argument]

From: Michael Kifer <kifer@cs.stonybrook.edu>
Date: Sun, 25 Jul 2010 22:30:58 -0400
To: Sandro Hawke <sandro@w3.org>
CC: public-rif-wg <public-rif-wg@w3.org>
Message-ID: <20100725223058.07e7c8e5@kiferserv>
OK, I think I am getting closer. You should have started with this.
So, it is not a matter of inference and its completeness but rather
of which rule exactly a particular RDF graph encodes, right?

That is, if we do not use lists explicitly in RDF then there is no way to encode

    a&b&c=>d

correctly? That it will be instead be encoding a set of rules that in addition
includes  a&b=>d, a&c=>d, a=>d, etc.

This looks like a strong argument. I haven't thought about it.

Dave, Harold, do you see a way around this problem?

michael


On Sun, 25 Jul 2010 22:10:52 -0400
Sandro Hawke <sandro@w3.org> wrote:

> I think we're misunderstanding each other.   It's possible I'm just
> wrong (as you seem to think), but I don't think so.   I can try to
> refine my language, but it's not clear to me how to do that right now.
> 
> So let me try a completely different line of argument for a minute.
> Please try to read between the lines of my poor command of the language
> of philosophy and formal logic:
> 
>   1. RDF is a KR.  An RDF graph is a logical statement; it makes claims
> about some world.
> 
>   2. If someone makes a claim by stating RDF Graph G, they are implying
> all the claims made by all the graphs entailed by G.
> 
>   3. While there may be some debate about which logics (and therefore
> which entailments) are appropriate/standard, RDF Simple Entailment
> certainly is.  So whenever you say something as an RDF Graph G, you are
> implying all the claims of all the subgraphs of G.
> 
>   4. Assume we have the RIF rule, a&b&c=>d, and it's encoded in graph G
> as node R. This means the agent stating G is claiming that R says
> a&b&c=>d.  
> 
>   5. If we use the repeated-properties mapping for that step-4 encoding,
> then there will be subgraphs of G which describe R as saying a&b=>d,
> a&c=>d, a=>d, etc.  
> 
>   6. If the agent stating G is also asserting R, then (by #5) the agent
> is also implying a&b=>d, a&c=>d, c=>d, etc.    If c is true, the agent
> will have implied d.   Consumers trusting that agent may justifiably
> infer d.  If it turns out a or b was false, this conclusion is wrong.
> So, this is bad.
> 
>   7. With the list-style mapping, the only subgraphs of G in which R
> encodes a RIF Document are those in which that encoded document has the
> same RIF meaning.  This is because the list-style mapping is essentially
> fragile; all the non-trivial subgraphs simply don't describe a RIF
> document.   So we avoid #6 badness.
> 
> I'm sorry I don't know how to say this in the proper mathematical
> language.  I hope it still makes sense.  Let me know which steps I need
> to expand on/clarify.
> 
>      -- Sandro
Received on Monday, 26 July 2010 02:31:32 GMT

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