Using integrity constraints to provide intensional answers to relational queries
A. Motro · Very Large Data Bases · 1989
An intensionalanswer to a query is a set of characterizations of the set of database values that satisfy the query (the extensional answer). Intensional answers provide users with additional insight into the nature of standard extensional answers. In this paper we describe a method that applies database constraints to generate intensional answers. These intensional answers characterize the extensional answers in two ways: (1) with constraints that are applicable to the extensional answer, and (2) with database views that are contained entirely in the extensional answer. Our method is to represent the definitions of constraints in special “meta-relations”, and extend standard algebraic operators to these relations. When a query is presented to the database system, it is performed both on the actual relations, resulting in an extensional answer, and on the meta-relations, resulting in definitions of constraints that apply to the extensional answer, as well as database views that are contained entirely in the extensional answer. These definitions are translated into an intensional answer that accompanies the extensional answer.