Algebraic Operations on Restricted Cardinality Sets in Relational Databases

A number of approaches have been taken to incorporating sets in relational databases. We review three such approaches and discuss a new approach, called restricted cardinality sets, which combines aspects of the other approaches, allowing both compound values and incomplete information to be represented. We show that this approach generalizes the other approaches, leading to a simpler, more flexible representation; and discuss the definition of algebraic operations on such sets.