Re: modelling issue?

Pat, and all, (incl offlist)
thanks for additional comments

For those who like the short answer, I am lead to think that what I consider
'worries' and possible conflicts or contradictions, probably fall under the
category 'known RDF limitations', widely discussed here and elsewhere. It is
also possible that RDF may not be appropriate either for what I was thinking
of (need to consider if OWL would make things better in my case, must look
into it)
I also think there may be some communication issues in describing it, since
I have had a variety of
comments each saying something a bit different,
and possibly 'all true' (or most true, or not, gotta check)

This could lead to a question 'do we have to live with this, and find
workarounds to limitations ' (can do :-)
or
is there something that can be done to address the limitations in future
generations RDF?

Since , Pat, your explanation is neat, and compact
I 'd like to slice it up a bit more, and get you to explain a few more
things, (I see some creases, perhaps you can iron them out for me)

But can't now, should be somewhere else, terribly late and away for a couple
of days, will be back :-)

cheerps

P

On Mon, Sep 28, 2009 at 6:10 PM, Pat Hayes <phayes@ihmc.us> wrote:

> I hesitate to get involved, but here goes...
>
> On Sep 27, 2009, at 6:07 AM, Paola Di Maio wrote:
>
>
>> During Vocamp Glasgow, I tried to confront my difficulties in identifying
>> some domain range of few vocabularies that I started rdfizing as practice,
>> and from explosing my questions to a whole range of RDF doctors (thanks
>> Norm, Keith, Serge) two things emerged, that i did not know before
>>
>> 1) an entity (class, object, subject) does not necessarily have domain
>> /range
>>
>> Is that so, and what's the rule/ and possibly exceptions/ that can be
>> inferred and applied?
>>
>
> In RDF, domains and ranges belong to properties (the things in the middle
> of the triples). The idea is that if the domain of P is D and the range of P
> is R, then when you write a triple
>
> a P b .
>
> then you are implying that a is in D and b is in R. Obviously D and R have
> to be classes. For example, the domain and range of motherOf might be
> respectively Woman and Human, so that if I write
>
> Betty motherOf Pat .
>
> you can infer that Pat is human and Betty is a woman.
>
> That is the full story on domains and ranges in RDFS (and in OWL, for that
> matter). So I'm not sure what you mean by the domain/range of an *entity*.
>
> BTW, there is no RDF requirement that domains and ranges be specified. You
> can just say nothing about them unless you want to. And you can give
> something two (or more) domains or ranges, and then the above constraint
> applies to both of them, eg a has to be in D1 and in D2 if they are both
> domains of P.
>
>
>> that did not emerge at Vocamp
>>
>>
>> 2) Apparently a triple can be of two kinds
>>
>
> Well, no. There is only one kind of triple in RDF. However, the third item
> in it can be a URI or a literal, indeed. This only really seriously matters
> in OWL, which gets very anal about the literal/non-literal distinction.
>
> :
>>
>> class:relation:class
>>
>>  but also
>> class:attribute:value
>>
>> Of this i would like some confirmtion (is this right?
>>
>
> No. Or at any rate, not if I am following you. First, the first item
> (subject) of the triple isn't necessarily a class. Second, the terms
> 'relation' and 'attribute' are not used in RDF, though they are both used
> more widely to mean what RDF calls a property.
>
> ),
>> Finally,  finally, wouldnt' this ambiguity be confusing?
>>
>
> There is no ambiguity. Relation = attribute (= property), so those are the
> same; and the only RDF-meaningful distinction for the third item is between
> a thing denoted by a URI, or a thing denoted by a literal. The latter is
> often called a value, but a value can be denoted by a URI as well, so thats
> not a distinction in kind so much as a distinction between two ways to refer
> to something.
>
>
>> i dont have a case study for this yet, but if this is true I suspect it
>> could cause some possible  logical conflict/ambiguity
>> in semantic data model and its implementation
>>
>
> From your message, I cannot see what distinction you are wanting to
> address. It is true that RDF is a very weak language and cannot express or
> represent all kinds of subtleties, but this does not make it ambiguous or
> conflicted. The RDF semantics is quite clear and unambiguous. Can you give
> some examples of the kind of contrast you have in mind here?
>
> Pat Hayes
>
> am I the only one thinking so?
>>
>
>
>>
>> Are the above points addressed in some RDF tutorial
>>
>> please enlighten!
>> thanks a lot
>>
>> PDM
>>
>>
>>
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-- 
Paola Di Maio
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Networked Research Lab, UK

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