| OCR Text |
Show CHA P TER 2 BACKGROUND 2.1 Requireme nts of Today's Applications Most CA D/CASE p rojects involve a group of des igners working toget her on t heir individual workstat ions to complete a design by interacting with others and dy na mi ca.lly sha ring design datil . T hese designers a re trying to model and design < u!llp ll'x !:iystems. T he real world consists of lots of ent it ies which a re int r icately i IIL<T-re la.tecl . T his means that the database schema t hat is used fo r t his kind of desig11 d;.-li,a lll usL l l <' ah le to n-~Aect t hese relat ionships. Object-o ri ented p rogramming vviLl1 its inheri tance hi era rchies, object composit ion, and polymorphism allows a programnwr to realist ically represent complex design information . These CAD/CASE app li cations are highly data-intensive and evolve incremen- 1 <til y. T l1is requires nJana.ging h1tg<' V<l!lti1H'S of claL1 allCI meta-data (informat ion <~iHJIIi ( l](' data), like owner!:il1ip, t ime of creation , update hi stories, inter-data relaLiuns hips, lock status, vcrs iou, etc. Moreover, t l1e clctta may need to be distt·ibu ted over heterogenous platforn1s, due to the dist ri buted nat u re of the euginee ri ng comp utat ion . To support <~ vo lu t i o n of data, t he data should be versionable, so tbat diffe rent versious of t he same claJa lll(I.Y co-exist and data updates do not res1il t i11 tlw oV<··rwrit ing of old daLa.. This leads to the issue of managing ve rsions. Since t li('s<' <t!Jfl licatic)l]s arl' genera.lly of long duration , flexi ble locking mechanisms should lw provided so tl1at thcs<: app li cations are not requi red to wait for each ot her for long period s. Applicat ions which 11sP in teract ive graphi cs must have fast access to |
