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From: marick@cs.uiuc.edu (Brian Marick)
Newsgroups: comp.object
Subject: Re: Survey: how do we really use objects?
Message-ID: <marick.660236973@m.cs.uiuc.edu>
Date: 3 Dec 90 15:09:33 GMT
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Organization: University of Illinois at Urbana
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timm@runxtsa.runx.oz.au (Tim Menzies) writes:

>As to the above argument re plant/animal classification:
>Just what are those  hierarchies used for? Actually expert
>processing of significant biologically problems?  Or only as
>a learning tool for new biologists?  (I suspect  the
>latter.)

In my (very limited) understanding, biological taxonomies are not
"single inheritance".  They're closer to multiple inheritance, but I'm
not sure that's a good fit, either.  They are "polythetic", which
means:

1. There are a number of relevant properties.
2. Each property is possessed by large numbers of individuals.
3. No property is possessed by every individual.

This means that there is no abstract archetype.  The search for one
can lead to an explosion of categories, one for each possible (or
noteworthy) combination of properties, with a complicated and
seemingly arbitrary inclusion structure (as you pointed out).

Here's a reference I had lying around:

Rodney Needham.  'Polythetic Classification: Convergence and
Consequences'.  Man, Vol. 10, No. 3, September, 1975, pp. 349-369.

Brian Marick
Motorola @ University of Illinois
marick@cs.uiuc.edu, uiucdcs!marick


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