Construction of relations in relational databases

Using a nonprocedural language for query formulation requires certain automatization of a query answering process. Given a query for creation of a new relation, the problem is to find an efficient procedure which produces this relation from a given relational database. We concentrate upon sequences of join operations which losslessly produce a relation required by a query. A new property of such sequences is analyzed which provides a basis for the presented algorithms that construct an efficient join procedure. The algorithms have polynomial complexity. A modified AND/OR graph is used for the display of a given set of dependencies and a collection of relations representing a database.