Logical foundations of active databases

Classical database management systems (DBMSs) have been enhanced over the past fifteen years with the addition of rule-based programming to obtain active DBMSs. Active behavior is mainly characterized by a rule language and an execution model. Execution models go hand in hand with advanced transaction models (ATMs) which relax the so-called ACID (Atomicity-Consistency-Isolation-Durability) properties. Both rule languages and execution models have been proposed in an ad hoc way to deal with applications which are not easily implementable using the classical DBMSs. Therefore an open problem in this area is to formally account for active behavior using a uniform formalism.; This thesis gives logical foundations to active databases using the situation calculus, a logic for reasoning about actions. Our approach appeals to theories in which one may refer to all past database states. We give a logical semantics to an ATM by specifying this as a theory of the situation calculus called basic relational theory, which is a set of sentences suitable for referring to past database states in the context of database transactions. We express the properties of the ATM as formulas of the same calculus. Such properties are logically entailed by the basic relational theory that captures the ATM. We illustrate our framework by formalizing various transaction models. Next, we introduce active relational theories , which extend basic relational theories by capturing typical aspects of active behavior found in existing active DBMSs. We give a formal semantics to various features of active behavior by using active relational theories. We capture the most popular active rules, the Event-Condition-Action (ECA) rules, as programs written in a situation calculus based logic programming language that accounts for parallelism and we also write transaction programs transaction programs that have active relational theories as background axioms. We also classify various execution semantics for ECA rules. Finally, we give a method for implementing active relational theories in Prolog.