Pii: S0169-023x(02)00056-3

This paper introduces a new approach to database design theory. It presents the concept of partial functional dependency in the relational database framework. This new kind of dependency is an extension to the classical definition of functional dependency. The extension is carried out following two basic ideas. First, the new dependency works over relations (not over schemes). And, second, a relation can partially verify a classical dependency in the sense that only some tuples, called exceptions, break the dependency. Throughout this work, we use that dependency to decompose relations through a more flexible and general decomposition process, and by iterating this process, we find a mechanism to extract knowledge from the original relation. We also give algorithms to implement usual operations and relational system maintenance. 2002 Elsevier Science B.V. All rights reserved.