W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > February 2003

RE: RDF Semantics: Interpretations and Modelling

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 3 Feb 2003 15:03:36 -0600
Message-Id: <p05111b18ba6485616e9d@[]>
To: "Massimo Marchiori" <massimo@w3.org>
Cc: w3c-rdfcore-wg@w3.org, Ossi Nykänen <onykane@butler.cc.tut.fi>
>  > #1.) RDF semantics does not define interpretation for containers or
>>  collections (etc.). Since RDF semantics treats URIs as parameters, this
>>  means that RDF models containers can interpreted arbitrarily.

That is too strong. There is a clearly defined intended meaning for 
the rdf:Bag concept: it says that the container in question is a bag, 
and the container membership properties tell you what its members 
are.  The order in which they tell you this is irrelevant, since the 
thing is a bag. The key point however is that this information - 
about being a bag - does not impose any restrictions on formal 
interpretations which can be expressed as valid entailments. There 
are no valid entailments about rdf Bags that are not also valid of 
rdf Seqs; the rdf model theory isn't able to distinguish between bags 
and sequences; other, of course, than simply by asserting that some 
of them are called 'bags' and some are called 'sequences'. And this 
is not surprising, because this distinction only makes sense in a 
semantics which has a notion of state, so that it makes sense to talk 
about what happens if you RE-order the elements. RDF semantics is 
state-free. So this isn't a bug in the spec, or an omission; it is a 
reflection of a very fundamental semantic property of assertional 
languages, of which RDF is one.

>This seems
>>  to nullify the work and efforts spend on defining, e.g., the rdf:bag
>>  container

What work and effort? What definition?

>or rdfs:comment. (From the viewpoint of entailments, why bother
>>  using bag if it's "just" a URIref.)
>Ossi, this is the Bag/Alt issue, raised in May 2002:
>AFAIK never replied yet.
>Incidentally, the same wrong argument pointed therein appears again 
>in the current last call draft.

Im not sure which 'wrong argument' you are referring to. I stand by 
everything I said that is  included in the above-referenced message. 
In particular,

" If
_:xxx [rdf:type] [rdf:Bag] .
>  _:xxx [rdf:_1] <ex:a> .
>  _:xxx [rdf:_2] <ex:b> .
>  entails
>  _:xxx [rdf:_1] <ex:b> .
>  _:xxx [rdf:_2] <ex:a> .
>  then it also must entail
>  _:xxx [rdf:type] [rdf:Bag] .
>  _:xxx [rdf:_1] <ex:a> .
>  _:xxx [rdf:_2] <ex:b> .
>  _:xxx [rdf:_1] <ex:b> .
>  _:xxx [rdf:_2] <ex:a> .
>  and by suitable reordering, it will entail that ALL members of the
>  bag are in ALL positions."

is a correct argument, and your response to it is incorrect.


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Received on Monday, 3 February 2003 16:01:57 UTC

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