Horizontal decompositions based on functional-dependency-setimplications

Abstract

A new approach towards horizontal decompositions in the Relational Database Model is given. It is based on partial implications between sets of functional dependencies. This horizontal decomposition theory is especially useful for databases which must represent “real world” situations, in which there always are exceptions to rather severe constraints like functional dependencies (fd's).The functional-dependency-set-implication (fsi) generalizes all previous work on horizontal decompositions using partial implications between (single) fd's.The exceptions to a set of fd's are formalized using another new constraint, the anti-functional-dependency-set (afs). The membership problem is solved for mixed fsi's and afs', and a complete set of inference rules is given. The inheritance problem, i.e. which dependencies hold in the (two) subrelations generated by the horizontal decomposition) is shown to be solvable in polynomial time.