Object models for computer aided design

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2C t􁪽􋵥ere __ scrre􁪽􋴚􁪽􋵲rres a tendency to 􁪽􋵧gnore all e􁪽􋵦f􁪽􋵣c􁪽􋵥ency 􁪽􋵡a:tc:􁪽􋵥 exce􁪽􋴚􁪽􋴚 􁪽􋴚􁪽􋴚􁪽􋵡an facters an􁪽􋵴 to assurre' =ha: sorre hierarchy of lower level abstractions. If the eff􁪽􋵣c􁪽􋵥e􁪽􋵴t irr;lemen􁪽􋵡ation 􁪽􋴚􁪽􋵬ll be found to rrake the scte􁪽􋵥e practical. T􁪽􋴚􁪽􋵳s can, in fact, be a valid approach, but the t􁪽􋵲rcen o􁪽􋵰 proef lies clearly witt those 􁪽􋵨ho propose such a sys:err.. Clarity a data definiti􁪽􋵮n language is a comffiunication medium between some person and some co􁪽􋵰puter system. If a person has a data object abstraction he wis􁪽􋵥es to represent, he must 􁪽􋵡ap that a􁪽􋵳stract􁪽􋵯o􁪽􋵣 cntc SOffie reFresentat􁪽􋵯on space. It :'s also necessary fer ttat person, or sorne other person, to be able te look - .... c ... the representat􁪽􋵯on and the associated Clarity is a measure of how well a Ferson can use, uncerstc􁪽􋵤d, ano 􁪽􋵦f necessary, modify a 9ive􁪽􋵲 re􁪽􋵲re5ention. For 􁪽􋵮nstance, a person may think of some abstraction as a" representation scherre 􁪽􋵡as no good way to represent this r e La t i ons n i p then it lacks the structural properties necessary for clarity. Since much inforffiation is context dependent, a representation scherre which tends to extract infor􁪽􋵡at􁪽􋵯or. from its proper context and "scatter" it, lacks