Point-based temporal extensions of SQL and their efficient implementation

Abstract. This chapter introduces a new approach to temporal exten-sions of SQL. In contrast with most of the current proposals we use single time points as references to time, while still achieving efficient query eval-uation. The proposed language, SQL/TP, naturally extends the syntax of SQL/92: it adds a single new data type that represents a linearly ordered universe of time instants. The semantics of the new language x-tends the standard SQL in the expected way: the new data type behaves identically to the existing types. We also eliminate or fix many of the problems connected with defining a precise semantics in interval-based languages. In addition we provide an efficient query evaluation proce-dure based on a compilation technique that translates SQL/TP queries to SQL/92. Therefore xisting off-shelf database systems can be used as back-ends for managing temporal data. 1 Why yet another temporal extension of SQL? After more than a decade of research in the area temporal databases there is stil