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Re: RDF Concepts and Abstract Data Model: semantics

From: Jerome Euzenat <Jerome.Euzenat@inrialpes.fr>
Date: Fri, 6 Sep 2002 16:20:24 +0200
Message-Id: <a05111b07b99e2c499959@[194.199.20.189]>
To: pat hayes <phayes@ai.uwf.edu>
Cc: www-rdf-comments@w3.org

Hello Pat,

In your message (Re: RDF Concepts and Abstract Data Model: semantics) 
of 05/09/2002,
you wrote:
>>| To serve this purpose, certain meanings of RDF statements must
>>| be defined in a very precise manner
>>
>>why "certain" and which ones?
>
>Good question. Most of them, but not all: there are some constructs 
>in RDF which cannot be given a coherent model theory (without 
>enormous effort), but nevertheless are already in widespread use, so 
>are being preserved in order to not interfere with 'legacy' code. 
>These include the reification constructs, for example. (I know that 
>one *could* give an MT for reification fairly easily, but that 
>meaning would not in fact coincide with the legacy uses, which are 
>more to do with tagging than true meta-description.)

OK, so it is just a matter of changing "certain meanings of RDF 
statements" to "the meaning of certain RDF statements", no?

>>>  A particular world is called an interpretation, so that model 
>>>theory might be better called 'interpretation theory'.
>
>Yes, I know that is what 'model' means in model theory, but 
>throughout the rest of the English-speaking world it means almost 
>the exact opposite: that is, a 'model' is usually taken to be 
>something (often something inside the computer) which is simpler 
>than a 'world' and is used to model it, not as meaning the world 
>which is modelled by the description. The very term 'data model' in 
>the title of the document uses it in this way, for example. This 
>unfortunate mismatch between the use of 'model' in mathematical 
>logic and its use throughout most of computer science (and in fact 
>science and engineering  more generally) regularly leads to tangles 
>of confusion, which is why I deliberately avoided the use of the 
>word in the RDF MT documentation, and referred instead to 
>'satisfying interpretations'. More long-winded but far less 
>confusing.  The next version of the RDF MT document will not even 
>use 'model theory' in its title.

OK, "satisfying interpretations" is fine there too.
But the assertion that model theory should better be called 
interpretation theory (something that I could endorse after a long 
discussion), goes a bit too far in that introduction, no? (especially 
since I can interpret this the way I did).

>>Also in 3.5 RDF graph, in the Note:
>>- RDF Graphs are "node-labeled, edge-labeled directed multi-graphs" 
>>(with no disjointness constraints between node-labels and 
>>edge-labels): the multi- aspect is not in the note (i.e., that 
>>there can be several arcs between the two same nodes -- maybe with 
>>different labels).
>>
>>Just for being nitty-gritty,
>
>Right, getting the graph terminology straight has been a hassle. I 
>myself now prefer to simply define it as a set of triples, and 
>relegate the graph terminology to the realm of graphics.

This was for remarking that the note is not aligned with other parts 
of the document which mention this (multi-) possibility.
-- 
  Jérôme Euzenat                  __
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  France____________________/                Jerome.Euzenat@free.fr
Received on Friday, 6 September 2002 10:20:35 GMT

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