Object models for computer aided design

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103 t􁪽􋵥e 􁪽􋵯o􁪽􋵥e! definition is re􁪽􋵲re!ented by oejects and O􁪽􋵪ject and a:::􁪽􋴚􁪽􋴚􁪽􋴺:e 􁪽􋴺:ruc:ureE ar􁪽􋴚 􁪽􋵥ell Eu􁪽􋵴ted for self d􁪽􋵳scri?tion. Tte 5che􁪽􋵡a :tself should be stered as 6e5cri􁪽􋵴tor otjects, attribu􁪽􋵥e descriptor oejects, and field des:r􁪽􋴿?􁪽􋵯or attrib􁪽􋵴tes, one ca􁪽􋵢 bootstrap to the 􁪽􋵯oint 􁪽􋵨here 􁪽􋴺::rib􁪽􋴚􁪽􋵥eE an􁪽􋵣 ca􁪽􋵢 be 􁪽􋵡a􁪽􋵩i?􁪽􋴡!ated 􁪽􋵩ith the sarre operations 􁪽􋵳se􁪽􋵴 to 􁪽􋵡ar.dle ir.stances 0: t􁪽􋵥ese objects and attrib􁪽􋵴tes. The Fortran c2sed system described in Appendix I 􁪽􋵡as 􁪽􋵲ri:t􁪽􋵮n 􁪽􋵯o5tIy in PCP-II 2sse􁪽􋵢bly language and together 􁪽􋵩ith the graphic scpport 􁪽􋵲rocessor required about three 􁪽􋵡a􁪽􋴭-months to i􁪽􋵰ple􁪽􋵥ent. Although record and set types 􁪽􋵥ere net irr;le􁪽􋵥er.ted, rrost of the essential concepts in this chapter are represented in this is;le􁪽􋵥entaticn. This irrplerrentation, and the exter.sive 􁪽􋵳se cf the i􁪽􋵰plementation of the predecessor system serve to d@TO􁪽􋴡!tr􁪽􋵴tE that these ideas are both consistent and reaso􁪽􋵡atle to implement and use. 4.13 SUffirr.ary the extensions 􁪽􋵥e 􁪽􋵡a􁪽􋵥e defined to P2sci1 and is given only to the point 􁪽􋵴tere it ir.tersects standard Pascal syntax (7J.