From: Pat Hayes (phayes@ai.uwf.edu)
Date: 10/08/01
>From: Pat Hayes <phayes@ai.uwf.edu>
>Subject: Re: new model theory for DAML+OIL
>Date: Thu, 4 Oct 2001 11:32:29 -0500
>
>[...]
>
>> >4/ My hope is that the RDF(S) model theory from the RDF Core WG will
>> >eventually include datatypes. If this is not the case then I expect that
>> >it will be able to admit the DAML+OIL version of datatypes.
>>
>> I would guess the latter is the likeliest outcome, but its only a
>> guess. Certainly I would want to at least achieve this as a minimum,
>> so let us try to keep our work in alignment as far as possible.
>>
>> It still seems to me that the slight weakening of the
>> ICEXT(I(rdf:Literal)) condition (to a subset of LV) is all that is
>> needed to keep the required compatibility, since my LV can be the
>> union of the ranges of your various literal mappings, and it may
>> overlap with IR (and if it does, then your two cases for rdfs:range
>> are both covered by my equation on the intersection.) If you
>> disagree, can you pinpoint the problem, so I can fix it?
>
>I don't think that this works, because mentioning a literal can make it
>also be a resource.
Inside the RDF WG, the term 'resource' is taken to be synonymous with
'entity' or
'thing'. Everything is a resource, in other words. Apparently you are
using the word in some other sense: can you articulate what your
understanding of 'resource' is?
>Consider
>
> rdfs:label rdfs:range rdfs:Literal .
>
> rdfs:range rdfs:label "Range" .
>
> makes I("Range") in ICEXT(I(rdfs:Literal)
> so <I("Range"), I(rdfs:Literal)> in IEXT(I(rdf:type))
> and thus I("Range") in IR
It has to be in IR, yes. And I think that is perfectly reasonable,
since IR is the universe of the interpetation. How about if I just
don't insist that IR consist only of 'resources' (which I took to be
simply a tautology, see above), but say that it is a set of
(resources and literal values)? Would that satisfy you on this point?
>However, there is also a more-basic problem with literals.
>
>Literals have a unique mapping into literal values,
I take is as a basic assumption of any denotational language that its
denoting expressions have a unique denotation in any interpretation.
If they don't, the language is too ill-defined to be useable to make
assertions with, as there is no way to know when two tokens are the
same expression or not. So yes, I do make this assumption, and I
insist that we must make this assumption; and if the formalism fails
to keep this true, then the formalism is so broken as to be unusable,
and needs to be fixed.
>which means the
>denotation of both literals below have to be the same.
>
> <Person rdf:ID="John">
> <age>05</age>
> <streetAddress>05</streetAddress>
> </Person>
That depends on what one counts as being the literal. If the literals
are simply the bare untagged numerals (or numeral strings), then
indeed I would say that we have to say that '5' denotes the same
thing wherever it occurs. But in this case, the obvious way out is to
say that some trace of the tagging is included in the syntactic form
of the literal, so that '5' tagged as an age and '5' tagged as a
streetAddress are *different* literals. That treats the tagging as
part of the syntax, which seems to me to be exactly and precisely
correct, since the tagging is usually referred to as METAdata.
If the useage of the term 'literal' in this community rules this out
as an option, then I will ask the WG to revise its nomenclature to
say that the 'literal' labels in an RDF graph be re-christened
'tagged literals' or some such.
>This would not allow one to consistently say
>
> <age rdfs:range xsd:integer>
> <streetAddress rdfs:range xsd:string>
>
Pat
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