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Re: I have a trouble with The RDF Model

From: pat hayes <phayes@ai.uwf.edu>
Date: Sun, 26 Nov 2000 14:15:41 -0600
Message-Id: <v04210101b64716f27be1@[205.160.76.86]>
To: Stefan Decker <stefan@db.stanford.edu>
Cc: RDF-Logic <www-rdf-logic@w3.org>
Stefan Decker, replying to Seth Russel, wrote:

>a triple is unique - nobody can distinguish
>between the triples [Bush, wonThe, Election]
>and [Bush, wonThe, Election] per se.

That is correct if 'triple' means an abstract mathematical object. 
However if these 'triples' are syntactic entities (kinds of 
expression) then one most certainly can distinguish two distinct such 
entities which have identical structure. This is called the 
"type-token distinction" in linguistics: its the commonplace 
observation that one can say or write the same 'thing' twice (two 
tokens with the same type).

>However, as you have already observed, the source of
>the triple might be relevant for believing a fact or not believing a fact.
>A model theory (assigning true or false)

That isnt quite what is meant by a model theory. (It would be a very 
trivial model theory.)

> therefore has to include the source of the triple.

No, the model theory simply assigns interpretations to the syntactic 
constructions; it does not control the syntax. If the 'at' 
construction is part of the syntax then the model theory should 
assign it a meaning, and if it is not part of the syntax then it 
should ignore it. So, is 'at' part of RDF syntax or not?

BTW, a model theory should assign a meaning (referent) to every 
well-formed expression of the language, so even if the language 
contains expressions of the form
([Bush, wonThe, Election] at RobustAI)
the question still arises of what exactly the subexpression
[Bush, wonThe, Election]
denotes, since it is not a truthvalue (it would probably be something 
like a function from the things denoted by the expressions after the 
"at" to truthvalues, ie a predicate on those things, whatever they 
are.)

>That means it should act on syntactic constructs like
>([Bush, wonThe, Election] at RobustAI)
>and
>([Bush, wonThe, Election] at Electoral College).
>These constructs are different even if the triples are identical.
>
>This violates neither the uniqueness of triples nor
>the Law of the Excluded Middle.

Yes, but you seem to now have changed the language into something 
else, and the original question (and this mailing list) is supposed 
to be about RDF. If someone asks whether there is an English word for 
"Schadenfreude", it isn't much use to tell him that there is one in 
German.

>One could vote to include the source of the triple into the RDF datamodel
>itself.
>Former discussion of this question in the rdf-interest group resulted in the
>expressed opinion to use reification for this purpose
>(see http://www-db.stanford.edu/~stefan/updates.html ).

I have a slightly more basic trouble with the "RDF Model". I really 
cannot understand what it is supposed to be a description OF.  Are 
these 'triples' to be considered syntax or interpretation? Since RDF 
has an XML-ish syntax which is quite different (it involves many 
angle brackets and quotation marks, for example), the 'triples' are 
apparently not the syntax. So I presume that they are intended to be 
part of the interpretation of the syntax, ie the semantics of RDF is 
defined in terms of abstract entities called 'triples'. But if that 
is so, then Stefan's reply to Seth, above, doesn't make sense, since 
obviously semantic interpretations aren't the kind of thing that can 
be located on websites, or which have 'sources' in this sense, or 
which are assigned truthvalues; and Stefan seems to refer to the 
model theory *of* the triples, rather than to the triples as 
constituting the model theory. So I am left completely confused about 
the meaning of RDF, as indeed I have been ever since first meeting 
it. I have been assuming in the DAML discussions that it is basically 
simply a syntactic specification (possibly the ugliest ever devised 
by any human being, but let that pass) without any actual semantics. 
However, some people seem to think that it has a semantics. Can 
anyone point me to a specification of a model theory for RDF? (Just 
to save time, there isn't one in: 
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#model )

Pat Hayes

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Received on Sunday, 26 November 2000 15:14:21 GMT

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