| OCR Text |
Show 39 AC=l y2 Figure 20: Ancestor Counts in a Dependency Graph. will be placed back on the Objects list again, so it is not necessary to push the object on the list at this time. H the ancestor count is zero, then all of the object's prerequisites are current and the object may be recomputed. The object's dependents now need to be recomputed so they are pushed onto the Objects list. This process is continued until the Objects list is empty. All of the objects which premise . the constraint network are current and the network may be satisfied. All of the objects which need to be recomputed but are not premises of the network are on the NextObjects list to be considered for recomputation during the next iteration. When topologlcaiEval is called with a non NIL constraint group, it implements constraintPremiseProp. As a special case, if the constraint group is NIL, topologlcaiEval will evaluate all of the objects on the Objects list, thus implementing postSatlsfactlonProp. |
