Knowledge representation using views in relational deductive data bases

Abstract

A logic-based data base system combines data manipulation capabilities of conventional data base management systems (DBMS) and theorem-proving capabilities of logic systems. A deductive data base system is a homogeneous logic-based data base system in which only one programming system is used for both data base access operations and inferential functions. Logic systems such as Prolog are convenient for representing deductive axioms. However, because they lack the data base processing efficiency of conventional DBMSs, they are inadequate for very large data bases. In this paper, we propose to investigate the capabilities of traditional relational DBMSs, such as those based on the language SQL, as deductive data base systems. Since deductive axioms generate information in the form of virtual relations, they have a strong affinity to views in relational systems. Therefore, we can readily represent deductive axioms as views in relational data base systems. We demonstrate that Horn clauses as well as data base integrity constraints can be formulated as views without difficulty. Deductive axioms involving negation can also be formulated as views, provided the set difference operator is used for negated formulas. However, since the transitive closure operator is not implemented in conventional relational systems, such systems cannot process recursive deductive axioms. Relational DBMSs can be rendered almost fully deductive by incorporating into their design recursive axiom processing abilities and better view processing techniques.