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Show 53 3. create a pcinter array for an "oer set" (e.g. and VC,!lY) • ... :-! :;. .. : case, i t i s clear that the ov e r h e e c to r e c r e s e n t a 2D3:-ec, sea=ate e':itv __ necessarily high. The source of this problem lies i the size cf the "sace" i n wh i cb these entities exist. In the rr ar.y s v s t err s ie.:;. D2TG s y s t errs ) this space i nc l ude s ase (i.e. ay record in the cata base er.tire cata rr.a y reference any ether record :n the data base). Some systerrs, such as the VD irrplemetaticn of APL partition the data base into a S IT a 11 n U :1. o e r 0 f s t :. III a r .q e II f i 1 e s II • However, VDAM files are typically several illion bytes so searching them for references to common entities is :'rrpractical in interactive environments. Vhenever the range of an exhaustive search is tco large to ake the searching strategy practical, it ::22 necessary to rcvide some sort of tack pointers cr emecdec rins structures for shared entities. As we noted in chapter 2, the actual cCr!ections fer a polyhedron and its faces, ?oir.:s forms a cluster about the polyhecron. inter-er,tity By rraking t;-.:':--.g5 like eases and po i n t s "e t t r i bo t e s " of an ·"objectll rather than indeendent entities, the overhead necessary for linkage can be greatly reduced. Since an attribute can net te cirectly referenced except from within the sae |
