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Subject: Seminar - On Visual Formalisms (CMU)
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Date: Tue, 3-Mar-87 10:23:53 EST
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	 		   PS SEMINAR

MONDAY, 9 March
WeH 5409
3:30


                     On Visual Formalisms

                          David Harel
                 Weizmann Inst., Rehovot, Israel
                     (At CMU for the year)

  A general mathematical object of diagrammatic nature, the higraph, is 
presented. Higraphs borrow and extend ideas from Venn-diagrams, graphs and
hypergraphs. They constitute a visual formalism for describing various 
kinds of complex entities, particularly those that involve many sets of
objects having intricate structural (i.e., set-theoretic) interrelationships
as well as additional relations af dynamic, causal or other nature.  

  Higraphs appear to have many applications, as well as a rich theory that 
awaits further research. We shall exhibit a number of applications in 
database theory (entity-relationship diagrams), artificial intelligence 
(semantic and associative nets) and concurrent reactive systems (statecharts). 
Statecharts constitute a natural extension of conventional state-transition 
diagrams in ways that make them appropriate for describing large real-world 
systems, and they will be described in the talk in some detail.

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