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Re: On equivalence of tidy/untidy (was: Re: Reopening tidy/untidy decision)

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Tue, 01 Oct 2002 16:48:05 +0100
Message-Id: <5.1.0.14.2.20021001164015.034d8010@127.0.0.1>
To: Sergey Melnik <melnik@db.stanford.edu>
Cc: w3c-rdfcore-wg@w3.org

At 10:24 AM 10/1/02 +0200, Sergey Melnik wrote:
>Our problem is that the entailment capability is *not* part of RDF 
>spec.    If it were, then we could define formally what the result of 
>entailment should be, applied to graphs. However, we do not require each 
>and every RDF application to support entailment (thanks God).

Entailment *capability* may not be part of the RDF spec, but certain 
allowable entailments *are*.  The fact that RDF permits certain entailments 
is not the same as saying RDF requires applications to deliver those 
entailments.

>Recall that entailment is a syntactic procedure, more precisely, a binary 
>relation that holds between syntactic sentences (graphs, in our case).

?!?  I thought entailment was precisely a *semantic* relation, defined in 
terms of truth of expressions (graphs) (which I grant are syntactic 
entities) under any interpretation.

>Defining entailment (in terms of logical inference) is comparable to 
>defining the semantics of a query language, like SQL. At this point of 
>time, we do not force every RDF application to support a specific query 
>language (which we could use to test tidiness)...

"Defining entailment (in terms of logical inference)" sounds line an 
oxymoron to me.

But I agree that we don't require all applications to find all valid 
entailments.

In fact, I don't think we require applications to do anything (though it is 
sometimes convenient to describe aspects of RDF by characterizing our 
expectations of applications -- I thought the whole idea of the formal 
semantics was to be able to nail down RDF meaning without having to 
describe applications).

#g


-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Tuesday, 1 October 2002 15:06:35 EDT

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