Object models for computer aided design

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56 􁪽􋵊Jss􁪽􋵴tly f:: :nto a pro􁪽􋵲rarr'5 􁪽􋵯orks􁪽􋵡ace, syste􁪽􋴬, tra􁪽􋴵5fers the sElected data object into to 􁪽􋴽=og=a􁪽􋵭 must f􁪽􋵲rs: access some ?ar􁪽􋵯 of the model. 􁪽􋵨he a::ess fun:t􁪽􋵣c􁪽􋴬, w􁪽􋴚􁪽􋵣ct 􁪽􋵳s prov􁪽􋵤dEd as part of the prograrr's works?ace. 􁪽􋵨he program 􁪽􋵡ay access various parts of the 􁪽􋵯odel, rean􁪽􋵰pulate the data objects in its workspace, an􁪽􋵵 u?date any tata otject 􁪽􋵨h􁪽􋵣ch has bee􁪽􋵣 chan?ed. The u?6ate functio􁪽􋵴 transfers a 6ata object frorr the workspace 􁪽􋵡ack i􁪽􋵴to the model. Frc􁪽􋴺 :􁪽􋵩is perspEctive it is clEar that the choice of t􁪽􋵥e size a􁪽􋴶6 structure of the "data objects" into which the rrodel is partitioned is a critical design decision for If the partitioninq is too coarse, a􁪽􋵣c :ne 􁪽􋵡a:a o:jec:s too large and co􁪽􋴚􁪽􋵬lex, they rray not through the un-needed inforrraticn to find that which is 􁪽􋴲2􁪽􋴺:􁪽􋵤d are likely to be Exc@ssive. On the other hand, if tre partitioning is too fine and the dat􁪽􋵯 objects are too small, the applicat􁪽􋵯on progra􁪽􋵲 rray have tc aCCESS a larqe number of thEse little pieces in order to construct a 􁪽􋴚􁪽􋵳s􁪽􋵩i􁪽􋴚􁪽􋵦f􁪽􋵬l !trccture on which to C􁪽􋵅Erate. Furtherrrore, since 􁪽􋵵uch mea􁪽􋵩ing is context dependent, a partitioning schewe 􁪽􋵨hlCh is so fine that it extracts information from its 􁪽􋵲ro?er context 􁪽􋵡ay tend to blur or co􁪽􋵰pletely destroy