Cycles in Structures of functional Dependencies

The main tasks of optimization of structure of the functional dependences (FD) between attributes of a relational database are considered: the task of creation of an optimum elementary base of structure of the FD between attributes and the task of search of optimum composition of the tables of the database which are in the third normal form. The optimum elementary base of structure of the FD between attributes contains the minimum quantity of the FD and the minimum quantity of attributes in them. The optimum composition of tables of the database contains the minimum quantity of tables. The review of methods of the decision of tasks of optimization of structure of the FD between attributes based on search of – dependences in an elementary base of structure of the FD and search of the generated complete substructures of structure of the FD having more than one key is provided. The concept of a cycle of an elementary base of structure of the FD is entered. Necessary conditions of existence of – dependences in an elementary base of structure of the FD both necessary and sufficient conditions of existence of the generated complete substructures of structure of the FD having more than one key are received. As a result the considered tasks are consolidated to tasks of search and the analysis of cycles in an elementary base of structure of the FD.