Aggregates in Constraint Handling Rules

Aggregates. We propose an extension of CHR with aggregate expressions in the heads of rules. Aggregates accumulate information over possibly unbounded parts of the constraint store. We provide a wide range of predefined aggregates, including all aggregates commonly found in related paradigms such as database query languages [1] (i.e. min, max, sum, count and avg) and production rule systems (i.e. not, exists and forall). The complete list of predefined aggregates, together with a number of example uses, can be found in [5].