Why to Use Deductive Technology in SQL Databases?

The notion of a deductive database has emerged during the 1970s in order to describe database systems capable of inferring new knowledge using rules. Within this research area three kinds of rule-based extensions for traditional databases have been intensively studied: active, deductive and normative rules. Nowadays, even SQL databases use these extensions in form of triggers, views and integrity constraints, although with quite restricted functionality. A uniform approach making these concepts really orthogonal to each other is still missing. In this paper we will show how new results in the eld of deductive databases may help to nd a more uniform extension of SQL. 1 Deductive Databases The notion of a deductive database has been used for systems capable of deriving new knowledge using deductive rules. These rules are usually expressed in the database query language Datalog because of its simplicity and readability. We will rst use this language for presenting important database concepts and transfer methods and concepts from Datalog to SQL later. A Datalog rule consists of a single positive literal called head of the rule and a conjunction of positive o