Gösta Grahne
Kari Jouko Räihä
ABSTRACT
Acyclic database schemes have attracted a lot of interest because of the nice properties enjoyed by such schemes. Recently some new acyclicity conditions that are strictly stronger than the normal α-acyclicity have been introduced by Fagin. Because of increased requirements, the database schemes in the new classes have some further useful properties that are not shared by α-acyclic schemes. Therefore the new classes have practical relevance.A database designer may work in terms of attribute sets and data dependencies, and not only in terms of database schemes. Thus it is important to have a characterization for the acyclic schemes of various degree in terms of data dependencies. For α-acyclic schemes such a characterization exists, but for the new classes the question has been open. In this paper we provide characterizations for β-, γ- and Berge-acyclic database schemes. The characterizations can be stated in a simple form: thus they should be useful for the database designer.
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