Question: Philip A. Bernstein, Barbara T. Blaustein, and Edmund M. Clarke. "Fast Maintenance of Semantic Integrity Assertions Using Redundant Aggregate Data" Proc. 6th International Conference on Very Large Data Bases, Montreal, Canada (October 1980). Presents an efficient method of enforcement for integrity rules of a certain special kind. An example is "every value in set A must be less than every value in set B." The enforcement technique is based on the observation that (for example) the rule just given is logically equivalent to the rule "the maximum, value in A must be less than the minimum value in B." By recognizing this class of rule and automatically deciding to keep the necessary maxi-mum and minimum values as hidden variables, the system can reduce the number of comparisons involved in enforcing the constraint on a given update from something on the order of the cardinality of either A or B (depending which set the update applies to) to one-at the cost, of course, of having to maintain the stored maximum and minimum values.