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Re: Necessary vs Necessary & Sufficient

From: Matt Halstead <matt.halstead@auckland.ac.nz>
Date: Tue, 20 Apr 2004 17:05:30 +1200
To: Stephen Rhoads <rhoadsnyc@mac.com>
Cc: www-rdf-logic@w3.org
Message-id: <58A3FC34-9288-11D8-AAA8-000A95B32AC4@auckland.ac.nz>

Necessary are conditions that must be met by and individual of a 
particular class, e.g. a Man must have the property of being human, but 
being human does not imply being a man.  With necessary and sufficient 
we have conditions that are both necessary, as in above, but then also 
sufficient for indicating inclusion in the extension of some class.  
E.g. a Man must have the property of being human and being male, we can 
use the intersection of human and male to form a necessary and 
sufficient condition, such that any individual that is male and human 
can be classified as a Man.

One trick is to think about having a large group of individuals 
exhibiting values for properties you find in various classes in your 
ontology.  You have no idea what they may represent, so you can at 
least start by going through and checking all necessary and sufficient 
conditions of classes against individuals to see if they classify as 
one or more of those classes.


On 20/04/2004, at 9:22 AM, Stephen Rhoads wrote:

> I would appreciate it greatly if someone could explain to me what the 
> difference is between a Necessary condition and a Necessary & 
> Sufficient condition.
> I would gladly RTFM if only I could find one.
> --- Stephen
Received on Tuesday, 20 April 2004 01:07:28 UTC

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