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Re: Comment on RDFa 1.1 Core: Profiles, term mappings, and URIs as literals (ISSUE-39)

From: Simon Grant <asimong@gmail.com>
Date: Thu, 12 Aug 2010 14:49:33 +0100
Message-ID: <AANLkTi=0H1scjYkBNngGBxE6kAXtQAC8de2J_ddyTzke@mail.gmail.com>
To: Richard Cyganiak <richard.cyganiak@deri.org>
Cc: Mark Birbeck <mark.birbeck@webbackplane.com>, Ivan Herman <ivan@w3.org>, public-rdfa-wg@w3.org
Please, may I hazard a pretty naive view of this, in the hope that a really
naive view from someone not at all involved in the detail might help? (It
will also help me to check my understanding...)

On 12 August 2010 13:59, Richard Cyganiak <richard.cyganiak@deri.org> wrote:

> [...]
> Now this is a trivially true statement:
>
> <http://xmlns.com/foaf/0.1/name> foo:uriLength 30 .
>
> While we have no evidence for the following statements (and hence can
> conclude they are false under closed-world reasoning):
>
> <http://xmlns.com/foaf/0.1/name> foo:uriLength 29 .
> <http://xmlns.com/foaf/0.1/name> foo:uriLength 31 .
>
> Look, I'm making statements about the lexical form of a URI.
>
>
>  * any properties we add to a URI concern the entity that URI
>> represents, and not the string of characters itself;
>>
>
> That is correct, but consistent with my proposed definition of rdfa:term.
> In RDF Semantics language, rdfa:term identifies the binary relationship that
> holds between an entity and a short form for the URI of that entity.
>

Richard seems to me to be implying, both through the use of the word "the"
in "short from for the URI of that entry" and in the use of the imaginary
predicate "foo:uriLength", that an entity has exactly one URI. If an entity
were to have exactly one URI, it would make some sense to enquire what its
URI is, or to make statements about its URI.

On the contrary, my understanding from this discussion is that various
people have emphasised that an entity is not in any way tied to a particular
URI -- that is simply a convention. Indeed, could I not easily have several
URIs (of different lengths, in this case) and assert owl:sameAs between
them?

In which case, what is put forward as a trivially true statement
"<http://xmlns.com/foaf/0.1/name> foo:uriLength 30 ."
could be unpacked (in English, let's ground this discussion outside RDF) as
* The FOAF concept of name is represented (by me) by a particular URI (even
though it might be represented by many other URIs).
* The URI that I use (at present, at least) for this concept has a length of
30.

But as others have pointed out, in the RDF world, where URIs stand for
things / concepts / whatever, how it is conceivable to have an actual URI as
the subject of a triple? Would it be reasonable to say that this is a
trade-off for RDF as a whole -- that we gain conciseness at the expense of
ruling out a whole area of expressibility?

I seem to recall that Topic Maps does this differently.

Presumably, to do this in RDF would require some special mechanism to
indicate that what is being talked about is a URI, not a thing that might be
represented by a URI, and we don't currently have that mechanism.

I hope this is at least a reasonable representation of the issue -- if not,
apologies and I will welcome correction.

Simon

-- 
Simon Grant
+44 7710031657
http://www.simongrant.org/home.html
Received on Thursday, 12 August 2010 13:50:02 GMT

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