Object models for computer aided design

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50 f􁪽􋴚􁪽􋴽=ly ccrr;!ex otject rray only re􁪽􋴚􁪽􋵩ire a fe􁪽􋴻 ;ar􁪽􋴚􁪽􋵥e􁪽􋵥erE. The 􁪽􋵡artit:o􁪽􋴺:r.g of t􁪽􋵥e data case in BCS is into Elemer.ts are described by their topology, qeo􁪽􋵥e:ry, and a set cif general a:tribu􁪽􋵥es. lar.s􁪽􋵡age GLIDE has been de􁪽􋵩ined to manipulate ele􁪽􋵥ents. k:though scs tss rrany of the sa􁪽􋵥e design goals ar.􁪽􋵢 basic ap;rcac􁪽􋵥es as the sytem to be defined, there are some ij.􁪽􋵣cr:􁪽􋵮nt fundamental differences. 􁪽􋴚􁪽􋵥e rr.cs􁪽􋵩 important difference goes back to the 􁪽􋵵u􁪽􋴵5:icn of the role of spatial infcrmation and graphic ir.teraction in a modeling system. In EDS the ccncepts of 􁪽􋵣c?clogy ar.d geometry are built into the b􁪽􋵳se level of the !ys:ern. Our approach will be to 􁪽􋵥efine a more g€neral case but y,·hicr. generally suited to graphic interaction, and then define a ;ra;hic s􁪽􋵰pport syste􁪽􋵯 on top of the base level syste􁪽􋴮. Different application areas rray require different 9raphic su?􁪽􋵯ort facilities􁪽􋵔 The factoring of common topologies co􁪽􋵬ld easily be an important efficiency measure ir buildinc 􁪽􋴚􁪽􋵅Ei;r., 􁪽􋵴tere many parts h􁪽􋵶ve s􁪽􋵡andardized shapes, but it serVES no purpcse in designing the arbitrary polyhedra needed to represent mining excavations. Ey clearly se􁪽􋵡aratin9 the base level syste2 for manipulating the data