# Re: modelling issue?

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 28 Sep 2009 12:10:17 -0500
Cc: semantic-web at W3C <semantic-web@w3c.org>
Message-Id: <214EFCF9-0D3A-4169-8317-40401A8729C6@ihmc.us>
```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
>
> thanks a lot
>
> PDM
>
>

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Received on Monday, 28 September 2009 17:11:41 GMT

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