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Date:         Mon, 9 Nov 1992 15:01:52 PST
From:         Penni Sibun <sibun@PARC.XEROX.COM>
Subject:      Re: Knowledge base; hierarchy & lnaguage
              7 Nov 1992 08:25:48 -0800 <92Nov7.082756pst.12057@alpha.xerox.com>

(penni sibun 921109.1400)


    [From Bill Powers (921107.0800)]

    Penni Sibun(921105.1300) --
    Avery Andrews (921106.1348) --

    I have some questions about the "knowledge base." I gather that what
    you mean by a knowledge base is a set of statements describing
    perceptions, rather than the perceptions themselves.

the kb doesn't know from perceptions.  it's just part of a computer
program!  you can think of the kb as made up of
propositions--essentially as in 1st order predicate calculus (w/o
quantification).  a prop. has the form:

(relation x y)  where x and y are objects or properties

examples are:

(father-of john penni)
(next-to kitchen livingroom)
(east-of livingroom kitchen)
(west-of kitchen livingroom)
(has-property livingroom-window large)

there's some annotations and bookkeeping hair (like the infamous
already-said? bit on objects) but that's pretty much it.

    I can see how it
    would be possible to mark a list of statements as "said" or "not
    said," but how would you mark the perceptions to which they refer?

there aren't any statements in the kb.  the kb contains objects,
properties, and relations (for no good reason than that is a classic
way of dividing up the a representation of the world that seemed
reasonable to me).  the kb is structured and interconnected by the way
the os, ps, and rs are combined in propositions.  while in principle,
you, as a human, can ``read'' the kb, a lot of the propositions in
salix's kb are never ``stated'', eg, (next-to-doors kitchen livingroom).

    In a lot of the proposals offered here by linguists, I get a sense of
    something missing. PCT itself is about how a brain works (whether
    we've got it right or not). So I'm always asking "how would the brain
    do that?"

i think what's happening here is a conflation in our discussion bet.
the program salix, which can be described precisely, and my
model/theory/whatever about how language works (which includes the
brain's role and whatever else).  in building a program to
demonstrate my theory, i wasn't trying to build an artificial brain,
i was building a demonstration that a system with thus-and-so
resources can do thus-and-such-a-thing.

    I think of a model as
    showing HOW something is done, even if only in principle;

i think my model *does* show *how* something is done.  definitely only
in principle, and certainly not at brain-level granularity.  my
argument that ``what can be said is codetermined by what has been said
and what there is to say'' sounds like a model of a process to me!  if
you don't think so, why not?

----

    Ed Ford failed to say that yearly membership in the CSG for students
    is $5. That's one reason the fee for working members is $45 --
    there's a subsidy.

somewhat beside the point, perhaps you can consider subsidising
unemployed people too.  i'm not suggesting you make an exception for
me, but there is a growing class of academics who are poorer than
gradstuds cause they have comparable income but are expected to pay
full price for everything!

cheers.

				--penni
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