On the Semantics of `Current-Time' In Temporal Databases

The notion of the current-time is frequently found in work on temporal databases, and is usually accessed via a special interpreted variable called now. Whilst this variable has intuitive and simple semantics with respect to the processing of queries in temporal databases, the semantics of the variable inside transactions has not been studied. With the growing maturity of temporal databases, and the need to construct production quality temporal DBMS to demonstrate the usefulness of the technology, it is necessary that a complete study be made of transaction processing in temporal databases. This work aims to meet this objective by (1) detailing the alternatives that exist in the evaluation of now, (2) studying the problems of using now in current transaction processing systems, and (3) provide a formal framework for the processing of temporal transactions, and give rules in the framework for avoiding problems in evaluating now. Keywords: Temporal databases, valid-time, transaction-ti..