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Possible movement from RDFS to RDF (was: Re: ACTION 20030425#4 [was Re: timbl-03])

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 5 May 2003 15:57:26 -0500
Message-Id: <p05210643badc78b95e7a@[10.0.100.12]>
To: fmanola@mitre.org
Cc: w3c-rdfcore-wg@w3.org

>Yes;  as noted in an earlier interaction with Brian, this also applies
>to RDFS.  As I said, the Primer would have to cover this point in some
>way (given that at the point where the Primer talks about Collections,
>it hasn't gotten to Schema yet).

Right. I felt a similar pressure, which is why there is a text 
comment in the RDF section saying that RDFS will add some more 
constraints to the RDF vocabulary.

The relationship between RDF and RDFS entailment is kind of sneaky, 
in fact. I put into the 'pure' RDF semantics all those conditions 
that could be stated 'directly' in terms of triples using just the 
pure  RDF namespace.  But this 'directly' is a delicate distinction, 
since one could state this condition without actually mentioning 
rdfs:domain, eg by imposing a semantic condition connecting 
rdf:first, rdf:type and rdf:List, without mentioning anything in the 
RDFS namespace at all

if <x,y> in IEXT(I(rdf:first)) then <x, I(rdf:List)> in IEXT(I(rdf:type)).

and similarly, by the way:

if <x,y> in IEXT(I(rdf:next)) then <x, I(rdf:List)> in IEXT(I(rdf:type)).
if <x,y> in IEXT(I(rdf:next)) then <y, I(rdf:List)> in IEXT(I(rdf:type)).
if <x,y> in IEXT(I(rdf:subject)) then <x, I(rdf:Statement)> in 
IEXT(I(rdf:type)).
if <x,y> in IEXT(I(rdf:predicate)) then <x, I(rdf:Statement)> in 
IEXT(I(rdf:type)).
if <x,y> in IEXT(I(rdf:object)) then <x, I(rdf:Statement)> in 
IEXT(I(rdf:type)).

Its just that this is all so much easier to say directly once the 
rdfs:domain/range is introduced, that it seemed kind of silly to 
write it into RDF, even though one could reasonably claim that these 
are all RDF rather than RDFS conditions, since they apply to the RDF 
vocabulary and can be stated as restrictions on it.  However, there 
isn't any reason why you need to be so fussy in the Primer, seems to 
me (??): you could just talk about things being in domains and ranges 
before formally introducing rdf:domain and rdfs:range. This would 
then allow you to introduce the idea when talking about RDF, then 
refer back to it to 'explain' what rdfs:domain and rdfs:range mean.

Or, if folk prefer, I could add these conditions to the RDF 
semantics, stated in the above style as semantic conditions, and 
supply appropriate RDF closure rules (which would of course be 
redundant in RDFS, but that's OK)

Any votes for this? It occurs to me that it might also help de-fuse 
some of the howls about reification and collections having 'no 
semantics'.

It would be quick to do at this stage, so don't feel that it would be 
a great slow-up or anything; and I could claim it as editorial since 
it really is only a matter of presentation, and nobody outside this 
WG is going to give a damn about the finer points of the RDF/RDFS 
distinction, I would guess.  If I hear two yeses and no noes, I'll 
put it into a revised draft :-)

Pat

>
>--Frank
>
>Graham Klyne wrote:
>>
>>  At 09:20 30/04/2003 -0400, Frank Manola wrote:
>>  >Or rather, whether this is true *in RDF* (as opposed to in OWL).  The
>>  >point is that, as I read the Semantics document, the only semantic
>>  >condition imposed on the collection vocabulary is that the type of rdf:nil
>>  >must be rdf:List.  This, of course, doesn't apply to the subject of an
>>  >rdf:first, so the inference Tim wants drawn would seem to be a semantic
>>  >extension which might be true for OWL, but not necessarily for RDF per
>>  >se.  It seems to me the explanation would have to cover this 
>>point in some way.
>>
>>  In the semantics doc, there's also:
>>
>>  [[
>>  rdf:first rdfs:domain rdf:List .
>>  rdf:rest rdfs:domain rdf:List .
>>  ]]
>>  -- http://www.w3.org/2001/sw/RDFCore/TR/WD-rdf-mt-20030117/#rdfs_interp
>>
>>  from which the rest flows through RDFS entailments.
>>
>>  #g
>>
>>  -------------------
>>  Graham Klyne
>>  <GK@NineByNine.org>
>>  PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E
>
>--
>Frank Manola                   The MITRE Corporation
>202 Burlington Road, MS A345   Bedford, MA 01730-1420
>mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-8752


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Received on Monday, 5 May 2003 16:57:28 EDT

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