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If the graph is changed by a production, the graph's consistency must be verified again. It would be very costly to test each time for all matches of possible structural constraints. Instead of this, instances of structural constraint types are memorized. These instances stay matched to a certain part of the constraint graph. Then, the graph must only be reverified with respect to the changes.

Whenever new elements are added by a production, there must be new structural constraint instances for all possible constraints' docking-part matches that include the new elements. Since there might be negative application conditions in the docking parts of existing structural constraints, those with an unsatisfied negative application condition due to the new elements must be excluded.

Whenever elements are deleted by a production, all structural constraint instances that matched these elements with their docking part must be deleted. If the deleted elements were part of a PAC in the docking part, the constraint instances must only be deleted if other elements to satisfy the PAC are not available. The deletion of elements may also mean that NACs of potentially applicable constraints' docking parts are no longer applicable. Structural constraint instances must be added in these cases.

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Last update:
May 20, 2001 by Alexander Nareyek