>Pat Hayes wrote:
>>>Pat Hayes wrote:
>>>>>Re: Peter F Brown's post (Sat, 14 Apr 2007 09:35:14)
>>>>>
>>>>>Peter writes:
>>>>>
>>>>>"
>>>>>The spec is clear, yesS. but an object is not the same thing as the
>>>>>address of the object - (according to the RFC, I *am* my address): the
>>>>>object needs identity as much as the address of it does. That is where I
>>>>>feel this axiom of the W3C falls downS
>>>>>"
>>>>>
>>>>>Clearly there is a problem here. But we should be careful to
>>>>>distinguish confusedly designed frameworks from confused documentation
>>>>>of well-designed ones.
>>>>>
>>>>>While RDF specifications, for example, are relatively clear and sound,
>>>>>the RDF primer provides an abundance of examples such as:
>>>>>
>>>>>ex:index.html exterms:creation-date "August 16, 1999" .
>>>>>ex:index.html dc:language "en" .
>>>>>
>>>>>supposed to state that "August 16, 1999" is the creation date of a page
>>>>>and "en" is he language of a page, while both are literal strings and
>>>>>*not* identifiers for a date and a language, respectively.
>>>>
>>>>What?? Why should a string not be an identifier? In fact, it
>>>>seems to me that *all* identifiers are strings. And the second
>>>>example uses a language tag which is taken from an Internet
>>>>standard for language tagging: what could be a better example of
>>>>an agreed identifier? Why is this confused?
>>>
>>>Hold on. It is not whether something is a string or not which
>>>counts, but how it is to be interpreted. Of course, "August 16"
>>>can be an identifier for anything you may wish. But it is a
>>>string, not a date.
>>
>>It *is* a string, of course. It *identifies* a date. You said it
>>was not an identifier, not that it was not a date.
>
>Yes, and I said that because this follows from RDF specs. A literal
>string appearing as the object of a triple is treated as a literal,
>i.e, as a self-referential entity, rather than an identifier for
>some other entity. In this context, "August 16" is not an
>identifier for a date, it is an identifier for itself. Is this
>better? (01)
In the RDF model theory, it denotes itself. But it may also be an
identifier for something else, using a system of identification
external to RDF. (02)
>>>But as the object of a triple, "August 16" is a literal, not a
>>>URI, and in RDF, a literal is (supposed to be) self-referential.
>>
>>Plain literals, yes. It would indeed be better practice to have the
>>object of that triple be a typed literal. But this is an example
>>from the *primer*; one step at a time.
>>
>>> Thus, the denotation of "August 16" is "August 16", not a date. Thus,
>>>
>>><u1> <u2> "August 16"
>>>
>>>effectively means that the denotation of u1 is in the denotation
>>>of u2-relation with "August 16" (the string), not with a date.
>>
>>But that string can be interpreted as denoting a date, using widely
>>used conventions for denoting dates. So this is a perfectly valid
>>RDF extension, speaking strictly, where 'extra' semantic conditions
>>are imposed (in this case, that the date-string is interpreted
>>conventionally). We anticipated that RDF would be widely used with
>>such conventions added.
>
>Can't see how this would be a good practice; for a dumb machine,
>you leave the question: is "August 16" supposed to identify a date
>(or whatever else), or is it supposed to identify "August 16"? (03)
The RDF machine, which is unusually dumb, can't tell. (It also
doesn't know that owl:sameAs means anything in particular, for
example.) But other entities using the formalism - some of which may
be machines which know other conventions - may. RDF isn't supposed to
be an AI Knowledge Representation language, standing alone and
supporting all notions of meaning. Its primary function is to act as
a means of transporting meaning rather than representing it. It would
be normal for RDF to convey some relationships using 'signs' to which
it - RDF - assigns no particular meaning. This is why we said that
plain literals denote themselves, rather than denoting an xsd string,
say: to ensure that no matter how much other specs (such as XML
Schema part 2) get re-written or amended, the exactness of a semantic
transfer using RDF will not be impaired. (04)
>While in this case you might use the range of the relation as a
>guidance, it may not always be so easy. Consider the case:
>
><text-uri> <contains-relation-uri> "the text 'hello'"
>
>Now, is "the text 'hello'" (replace single quotes with escaped
>double quotes if preferable) an identifier for "the text 'hello'" or
>for "hello"? It won't help that (the referent of)
>contains-relation-uri has the type 'string' as its range.
>
>My point is, it seems far better to say that a literal is
>self-referential rather than that it may or may not be, depending on
>some unspecified context. (05)
It is self-referential in pure RDF. But it may still identify
something else in a larger system of interpretation. RDF is not
intended to be incompatible with such larger uses: quite the contrary. (06)
Pat (07)
>
>
>vQ
>
>>
>>Pat
>>
>>>
>>>>
>>>>> But from
>>>>>this apparently confused example one should not infer that RDF itself is
>>>>>confused (in this respect).
>>>>>
>>>>>(This is not to say that RDF is not confused.)
>>>>
>>>>One can make many valid criticisms of RDF, but being confused
>>>>isn't one of them.
>>>
>>>I did not say that RDF was confused either. I just said I hadn't
>>>said it were.
>>>
>>>vQ
>>>
>>>>
>>>>Pat
>>>>
>>>>>
>>>>>
>>>>>Wacek
>>>>>
>>>>>
>>>>>
>>>>>--
>>>>>Wacek Kusnierczyk
>>>>>
>>>>>------------------------------------------------------
>>>>>Department of Information and Computer Science (IDI)
>>>>>Norwegian University of Science and Technology (NTNU)
>>>>>Sem Saelandsv. 7-9
>>>>>7027 Trondheim
>>>>>Norway
>>>>>
>>>>>tel. 0047 73591875
>>>>>fax 0047 73594466
>>>>>------------------------------------------------------
>>>>>
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>>>>
>>>>
>>>
>>>--
>>>Wacek Kusnierczyk
>>>
>>>------------------------------------------------------
>>>Department of Information and Computer Science (IDI)
>>>Norwegian University of Science and Technology (NTNU)
>>>Sem Saelandsv. 7-9
>>>7027 Trondheim
>>>Norway
>>>
>>>tel. 0047 73591875
>>>fax 0047 73594466
>>>------------------------------------------------------
>>
>>
>
>--
>Wacek Kusnierczyk
>
>------------------------------------------------------
>Department of Information and Computer Science (IDI)
>Norwegian University of Science and Technology (NTNU)
>Sem Saelandsv. 7-9
>7027 Trondheim
>Norway
>
>tel. 0047 73591875
>fax 0047 73594466
>------------------------------------------------------ (08)
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