This paper studies functional dependencies in Horn theories, both when the theory is represented by its clausal form and when it is deened as the Horn envelope of a set of models. We provide polynomial algorithms for the recognition of whether a given functional dependency holds in a given Horn theory, as well as polynomial algorithms for the generation of some representative sets of functional...

There is an increasing use of object oriented methods (e.g. [Ru91], [UML97]) for the design of database applications and databases themselves. Like the Entity–Relationship model and its variants, structural models of these methods provide rich modelling concepts for specifying object schemas. Some kinds of integrity constraints, e.g. referential integrity constraints or cardinality constraints ...

Functional dependencies are an integral part of database design. However, they are only defined when we exclude null markers. Yet we commonly use null markers in practice. To bridge this gap between theory and practice, researchers have proposed definitions of functional dependencies over relations with null markers. Though sound, these definitions lack some qualities that we find desirable. Fo...

Partial functional dependencies, functional dependencies accompanied by a factor, are examined in a relational database based on or-sets. The partial functional dependencies are dealt with under tuples having their belongingness degree to a relation. Whether a functional dependency accompanied by a factor holds in a relation is determined by comparing the factor with to what degree the relation...

The paper proposes a problem decomposition method for building optimal cover for a set of functional dependencies to decrease the solving time. At the beginning, the paper includes an overview of the covers of functional dependencies. There are considered definitions and properties of non redundant covers for sets of functional dependencies, reduced and canonical covers as well as equivalence c...