Sets and Uncertainty in Relational Databases

A number of approaches that have been taken to using sets to represent compound values and uncertain information in relational databases. We review three such approaches (collective sets, disjunctive sets and generalized sets), and propose a new approach (restricted cardinality sets), in which every set is accompanied by a range of possible cardinalities of the actual value represented. We show that this approach generalizes the other approaches, leading to a simpler, more flexible representation. We also consider defining algebraic operations on the sets.