Aggregation in Constraint Databases.
Gabriel M. Kuper · 1993
We show how to add aggregation to a constraint database query language. One example of the use of aggregation in such a database is computing the area of a region in a geographic database. We show how aggregation can be added to the algebra and tuple calculus, and discuss the problems that arise from the interaction of aggregate operators and constraints. 1.2 Introduction The idea of of combining relational databases with constraint formalisms is introduced in [KKR90] (see also [KG94] [Revesz90]). The key idea is the generalization of the notion of a tuple to a conjunction of constraints. One important aspect of relational databases that is missing in these papers is a discussion of how aggregate operators interact with constraints. In a standard relational database, typical aggregate operators are: sum, average, max and count. In a constraint database, besides these operations, we also want to compute functions such length, area and volume. Other possible aggregate operators include...