Functional Dependencies and Incomplete Information
Yannis Vassiliou · Faculty Digital Archive (New York University Florence) · 1980
Functional dependencies play an important role in relational database design. They are defined in the con-text of a single relation which at all times must contain tuples with non-null entries. In this paper we examine an extension of the functional dependency interpreta-tion to handle null values, that is, entries in tuples that represent incomplete information in a relational data-base. A compiete axiomatization of inference rules for extended functionai dependencies is also presented. Only after having such results is it possible to taik about decompositions and normalization theory in a context of incomplete information. Finally, we show that there are several practical advantages in using nulls and a weaker notion of constraint satisfiability. 1.