A Sound and Sometimes Complete Query Evaluation Algorithm for Relational Databases with Null Values

Abstract

A sound and, in certain cases, complete method is described for evaluating queries in relational databases with null values where these nulls represent existing but unknown individuals. The soundness and completeness results are proved relative to a formalization of such databases as suitable theories of first-order logic. Because the algorithm conforms to the relational algebra, it may easily be incorporated into existing relational systems. © 1986, ACM. All rights reserved.