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An alerter is a program which monitors a database and reports to some user or program when a specified condition occurs. It may be that the condition is a complicated expression involving several entities in the database; in this case the evaluation of the expression may be computationally expensive. A scheme is presented in which alerters may be placed on a complex query involving a relational database, and a method is demonstrated for reducing the amount of computation involved in checking whether an alerter should be triggered.
Buneman et al. (Sat,) studied this question.