A synthesis algorithm for a class of 4NF

• Authors: E. A. Unger;Cleopas O. Angaye
• Venue: ACM SIGSMALL/PC Notes
• Year: 1987

In order to ensure a better logical data base design that captures the semantics of the enterprise application, two basic approaches, decomposition and synthesis, are employed. The synthesis approach provides a schema that envelops all the given dependencies, though currently applicable to only functional dependencies and only for 3NF. However, the decomposition approach may produce data base schema in BCNF without satisfying the dependency preserving property [BEE79]. Ling et al. [LIN81] have discussed the existence of an objectionable form of attribute redundancy denoted superfluous attributes in schemas formed by decomposition and synthesis algorithms. A new synthesis algorithm, denoted Algorithm 2 [ANG83], eliminates such superfluous attributes from synthesized data base schema.In this paper, definitions for separable entities based only upon the dependency set under consideration are given. Algorithm 2 [ANG83] is shown to produce a data base schema which is in BCNF if the dependency set consists only of functional dependencies and the entities are separable. Further, a synthesis algorithm to normalize a relational schema involving only multivalued dependencies into a 4NF data base schema is proposed. The inclusion of multivalued dependencies in the synthesis algorithm permits wider units of information representation in the modeling of enterprise application. This algorithm will produce a 4NF schema if the dependency set consists only of multivalued dependencies which are not also functional dependencies and the entities are separable.