Pat Hayes wrote:
>> Pat Hayes wrote:
>>>>
>>>>>> , but we could say that u1 is the subject of the triple,
>>>>>> etc., but then we need to be clear in distinguishing the triple as an
>>>>>> expression and the proposition it expresses, of which u1 is not the
>>>>>> subject.)
>>>>>
>>>>> Right. The notion of proposition does not really get used in RDF.
>>>>> Although if you check the recommended semantics for reified
>>>>> triples, the reification is interpreted as a proposition rather
>>>>> than a syntactic expression.
>>>>
>>>> In the docs, you differentiate between a triple (in the abstract)
>>>> and a particular realization of it, in some physical document. This
>>>> is perhaps what you mean here, but this still does not seem to me to
>>>> be the distinction between a proposition and an expression.
>>>
>>> No, thats not what I meant. I was referring to the suggested truth
>>> conditions for reified triples, in which the (take a deep breath)
>>> object of the subject property is the referent of the subject URI of
>>> the original triple, not the subject URI itself.
>>> ...
>>
>> Still holding... Yes, this is clear from the (suggested) semantics of
>> the reification vocabulary. But I were far from even mentioning
>> reification.
>>
>>>
>>>>
>>>>>>
>>>>>> Note that an RDF(S) triple may have a literal rather than an
>>>>>> identifier
>>>>>> as the object. Using this form, you can explicitly connect a URI to
>>>>>> another URI, so that the latter is the referent of the former.
>>>>>> Although
>>>>>> the core RDF(S) vocabulary does not provide you with a URI for the
>>>>>> relation of identity, there is nothing in the way to create one.
>>>>>
>>>>> But this relation isn't identity, its more like 'refers to'
>>>>> (actually its inverse). BUt I agree, one can add this property. It
>>>>> can't be described in OWL or even in normal FOL, so one needs some
>>>>> external machinery or extension in any case.
>>>>
>>>> No, you're wrong here. Since the URI in the subject position is
>>>> treated as a reference and not as an entity, you can't make a
>>>> statement such as 'u1 denotes u2'.
>>>
>>> You can if you have a name for u1. Of course you cannot use the URI
>>> to name itself, but you had already noted that point (on which we
>>> agree, of course).
>>
>> What I was saying is that you the triple
>>
>> u1 u2 u3
>>
>> does not *necessarily* say anything about the URI u1; it may, though,
>> if u1 is self-referential (and why couldn't it be?) That is, there is
>> nothing in the RDF semantics that would forbid a URI to name itself.
>>
>> The *form* of the statement in RDF would be a triple like
>>>
>>> u3 denotes u2 .
>>>
>>> where 'u3' is the URI used to refer to the URI 'u1'. My point - and I
>>> think we are in violent agreement here - is that the relationship of
>>> naming, which has to hold between u3 and u1 in order for this to be
>>> any use, is something outside the RDF model. But this should not be
>>> surprising: RDF is very simple, and even its own reification
>>> vocabulary needs some kind of external machinery to connect the
>>> subject URI of the reification graph to the original triple which the
>>> reification is supposed to describe.
>>>
>>>> You need to make a statement such as 'u1 is u2', where the first
>>>> URI is dereferenced, and the other is not
>>>
>>> You can't do it that way (in legal RDF) as the RDF spec requires all
>>> URIs to be dereferenced.
>>
>> I do can, since a URI is just a sequence of characters organized
>> according to specific syntactic rules (this is a syntactically
>> modified but semantically rather accurate definition of URI). Thus,
>> the following triple has the effect of asserting that a URI is
>> self-referential:
>>
>> protocol://domain/some-name protocol://domain/identity-relation
>> "protocol://domain/some-name"
>>
>> where "protocol://domain/some-name" is a string literal which happens
>> to be a valid URI, the same as used in the subject (of the triple).
>> Thus, the referent of the URI protocol://domain/some-name is in the
>> relation of identity (say) with the string enclosed in double quotes
>> (which do not belong to the string!) -- that is the URI denotes itself.
>>
>> There is no quotation in RDF. Perhaps we should
>>> have put it in, but its too late now. In fact, reification seems to
>>> have died and not be widely mourned, so maybe this omission is not in
>>> fact of great importance.
>>
>> There is no quotation, but since URIs are strings, a string
>> indiscernible from a URI is in effect identical with the URI.
>>
>> But even if this fails, for some reason, you can use a URI to refer to
>> itself by just intending to do so, as you would intend to use a URI to
>> denote a dog, say.
>>
>> vQ
>
> Ahhh, I see now what you have been saying. Sorry if I was slow. Yes, you
> are right, in princiople we could have slef-referntial URIs, and their
> characteristic hallmark woul dbe that they were equal to their own
> quotations. (It would be better to use a typed literal with xsd:anyURI,
> which is unambiguously understood to refer to URI, even if URIs are
> considered different from strings (which they are by some people; giving
>
> protocol://domain/some-name protocol://domain/identity-relation
> "protocol://domain/some-name"^^http://www.w3.org/2001/XMLSchema#anyURI . (01)
This is exactly what I said in one of my first posts on this issue,
though I restrained myself from using the concrete syntax: (02)
<u1> <u2> "u1"^<uri> (03)
asserts self-referentiality of u1, provided that u2 denotes identity,
and uri denotes the xml-schema datatype anyURI (though this is optional,
I think). (04)
(Note that the triple above is in fact a triple with a nested triple
with a nested pair.) (05)
>
> But this cannot be a general solution, since most triples contain URIs
> whose intended interpretation is not themselves, but something that was
> the topic of the representation containing the triple in the first
> place. Making them refer to themselves will change their meaning, and
> the meaning of the ontologies that contain them. So what we need as a
> general device is a way to create a new URI (<u3> in my message) which
> refers to a given URI, i.e. in effect a quoting mechanism. Such a thing
> could of course be set up, by defining a 'uri-quoting' name space and
> forming the new u3 URI out of it and the old u1 URI in some systematic way.
>
> Im afraid I have lost track of what this purpose of this thread is :-) (06)
The initial purpose of my communications was to defend the thesis that
it is possible (at least in rdf) to make statements about uris in a way
that leaves no question whether it is the ur or its referent that the
statement is about. Someone complained that it is not clear whether an
expression involving a URI is about the URI or about its referent, and I
claim that, in RDF at least, it is clear: (07)
"<u1> predicate object" is about the *referent* of u1, and about a URI
iff the referent of u1 is a URI, and about u1 iff the referent of u1 is u1. (08)
Self-referential URIs are of little importance, I showed that you can
have such because you agreed with me that there cannot be
self-referential URIs in RDF. (09)
vQ (010)
>
> Pat
> (011)
--
Wacek Kusnierczyk (012)
------------------------------------------------------
Department of Information and Computer Science (IDI)
Norwegian University of Science and Technology (NTNU)
Sem Saelandsv. 7-9
7027 Trondheim
Norway (013)
tel. 0047 73591875
fax 0047 73594466
------------------------------------------------------ (014)
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