W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2001

RE: rdf as a base for other languages

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 4 Jun 2001 20:44:32 -0500
Message-Id: <v04210118b741e8ffbd3d@[205.160.76.219]>
To: "Ziv Hellman" <ziv@unicorn.com>
Cc: www-rdf-logic@w3.org
> > Similarly, there is no reason that you cannot have a language that can
> > express ground facts, and embed it in a different language
> > that can express
> > more.  However, the meaning of this larger language is quite
> > different from
> > the meaning of the smaller language.  (Consider how you would handle
> > ``facts'' with variables in them---you can't just use the
> > meaning from the
> > smaller language, as it has no idea how to interpret the variables.)
> >
> > Further, even this is different from having a language for expressing
> > ground facts (RDF), encoding more-complex constructs in this
> > language, and
> > using the ground facts language as the transfer mechanism.  Under this
> > scheme, the encoding of the more-complex constructs are still
> > viewed as
> > ground facts, and end up becoming part of their meaning,
> > which is not desired.
>
>
>I am beginning to lose sight of what the terminology "ground facts" 
>is supposed to mean in this context.
>
>At the risk of being a considered a dreary pedant, I will sketch out 
>here how I was taught one constructs a logic, and then ask where 
>this fits into the terms of the debate raging in this interests list:
>
>a.  Determine a group of "logical" symbols that are "reserved" and 
>assumed to be a part of any language that one will define and use -- 
>this is where connectives, quantifiers, modal operators, etc. are 
>declared, perhaps also variables
>
>b. Determine that a language may contain "non-logical" symbols that 
>play the roles of relations, or functions, or constants etc.
>
>c. Determine rules for deciding what constitutes a well-formed 
>statement built out of these logical and non-logical symbols
>
>d. At this point, either build a proof theory or a model theory or 
>both. For a proof theory, declare logical axioms and rules of 
>inference that enable one, given certain statements as assumed, to 
>infer other statements as conclusions. For a model theory, one needs 
>to explain how and when statements in the language are to be 
>considered "satisfied" in possible worlds or structures or models, 
>etc.
>
>What are "ground facts" this picture?

They are any sentences which either do not use quantifiers or free 
variables, or maybe (no serious logical difference) which only use 
pure existential quantifiers at the top level. More strictly, in RDF 
they are finite conjunctions of atomic sentences of the form (R a b) 
where R is a relation and a, b are names (or free variables, 
understood as existentially quantifed by top-level quantifers). (The 
sentence/fact terminological slippage is widespread and tolerated.)

Pat

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Received on Monday, 4 June 2001 21:44:45 GMT

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