# 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

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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