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From: wex@dali.pws.bull.com (Buckaroo Banzai)
Newsgroups: sci.virtual-worlds
Subject: Re: Who says what to whom (was Re: VR Protocols.)
Message-ID: <8078@milton.u.washington.edu>
Date: 24 Sep 90 17:28:10 GMT
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In article <7989@milton.u.washington.edu> xanthian@zorch.SF-Bay.ORG (Kent Paul D
olan) writes:
   wex@dali.pws.bull.com (Buckaroo Banzai) writes:
   >So what's the default value for something like "has a door I can walk
   >through"?  Do you see how much knowledge is presupposed simply in asking
   >that question?  This is what led me to want to separate out the real-world-
   >modeling aspects from the objects-that-implement-stuff aspects.

   But in the real world, nothing screams at me "has a(nother) door I can walk
   through" when I enter a room. What I get, with the aid of a lot of visual
   system processing is: "has a rectangular parallelopiped with a striated
   texture and two shiny cylinders on one side's edge and one white shiny
   circular object on the other".

I disagree strongly with you here.  See, for example, Don Norman's work on
affordances, particularly The Psychology of Everyday Things.  I know Don
reads this group from time to time - perhaps he'd care to comment.

   It is _my_ knowledge base/subsequent processing that classifies that as
   "probable door, two brass hinges, one enamel doorknob", with a possible
   alternate, subject to further interactive test, classification of
   "photorealistic painting".

My point is not "can you figure out there's a door there" based on sensory
input.  My point is that the fact that you're *looking* for a door indicates
that you've brought along a *huge* amount of "real-world" knowledge, not
least of which involves things like "hinges" and "doorknobs."  It's easy for
humans; we have years of learning this stuff.  However, trying to program it
into objects is, I contend, ultimately futile.

That was the major thesis of my opposition to the objects-interact-by-
sending-properties-around protocol.

   Similarly, while the building needs to know about my mass and physical
   extent and position, unless it contains mirrors, it is probably intensely
   uninterested in the fact that I can provide visual information, and it
   is probably inappropriate design to put that capability in the building,

But what if the building has windows through which you are being observed by
other users or by a visual recording device?  [Note again: I'm not saying it
can't be done.  I'm saying that you're heading for a world of trouble both
in terms of trying to give objects knowledge about the world, and in terms
of the number of special cases you're going to have to create.]

--
--Alan Wexelblat                        phone: (508)294-7485
Bull Worldwide Information Systems      internet: wex@pws.bull.com
"Politics is Comedy plus Pretense."