Join dependences and solutions of the projection synthesis problems in relational databases. II

The properties of joins of base relations are discussed in the case of developing a new relation («projection synthesis») in relational databases, RDBs, with a universal relation. The RDB flowchart is described by a reduced intersection graph which is then used in looking for solutions of the synthesis problem. The necessary and sufficient conditions are formulated for a subset of basic relations to be members in a set of solutions of the synthesis problem when no additional constraints are introduced in the RDB. Such constraints are shown to modify the reduced graph and give rise to new solutions.