Abstract: Preferred embodiments of the invention provide a system for, and method of, exploring relationships in data stored in a computer readable medium. Under one preferred set of embodiments, sets of data are maintained in a computer readable medium and include at least one intensional expression and one extensional expression of at least one set resulting from an evaluation of a first query. A second query is transformed into a set program. It is then determined whether a sub-expression of the set program is satisfied by a maintained set. If so, the sub-expression is removed from the set program and the maintained set that satisfies the sub-expression of the set program is used. Under another preferred set of embodiments, a query is received having at least one operator chosen from a set of operators that includes relational operators and having at least one input and output associated with the operator and defined as a table having at least one domain having a type associated therewith.