W3C home > Mailing lists > Public > www-rdf-logic@w3.org > December 2000

Re: Logic and Using The Semantic Web Toolbox

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Mon, 4 Dec 2000 10:02:43 -0500 (EST)
Message-Id: <200012041502.KAA18840@mr4.its.yale.edu>
To: www-rdf-logic@w3.org
CC: drew.mcdermott@yale.edu

   Pierre-Antoine CHAMPIN wrote:

      So you admit that (wins Bush election2000) does not have the same
   role when written alone, or as a nested expression.

      In the language you use, every outer parenthesis-pair makes an
   assertion ; inner parenthesis-pairs do not.

      In RDF, each arc of the graph makes an assertion. If you want to
   quote an arc without asserting it, you need to write/express it (in
   the graph) not as an arc. The chosen solution is reification.

I realize this is the model.  I don't understand the rationale for it,
or why the issue has already been decided.  (I also don't understand
why reification solves the problem; if it's supposed to be beyond my
control whether all subgraphs of G are asserted whenever I assert G,
why isn't it beyond my control to prevent the assertion of expressions
that are named without being uttered?)

I suspect that what happened was that (a) people thought the graph
model was cool; (b) they realized it has this bug (where's the top of
it?); and (c) they decided to try to do without the notion of "top of
the graph."  AI went through all this twenty years ago, but for some
reason no one opted for this solution, as far as I know.  The usual
solutions are:

(a) Introduce extra structure into the graph to indicate where the
actual syntactic boundaries are.  One way is the "partitioned
networks" of Gary Hendrix  Another is Stuart Shapiro's SNePS model,
which I believe is the one most thoroughly worked out.  I'm not an
expert in this area, but I think there are several experts involved in
this discussion.

(b) Relegate the graph model to secondary status.  The primary model
is in terms of strings, and the graphs are introduced as
implementation details (for indexing purposes, or to provide
special-purpose inference algorithms).  This is what CYC does. 

Maybe these approaches are just too hopelessly uncool for the
hyperwired web.

                                             -- Drew McDermott
Received on Monday, 4 December 2000 10:02:52 UTC

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