Point-based Temporal Extension of SQL

Most of the common proposals for temporal extensions of SQL (e.g., ATSQL2 or SQL/Tem-poral) use explicit interval-based references to time (interval attributes). In this paper we propose a diierent approach: we use point-based references to time as a basis for a temporal extension of SQL. The proposed language|SQL/TP|extends the syntax and semantics of SQL/92 in a very natural way: by adding a single new data type that represents the universe of individual time instants. Such an extension allows the users to write temporal queries in a customary fashion and vastly simpliies the semantics of the proposed language: we can essentially use the common SQL semantics. This way SQL/TP also xes many problems present in query languages that use explicit interval-based temporal attributes. In addition, SQL/TP queries can still be eeciently evaluated over a compact interval-based encoding of possibly innnite temporal relations. The query evaluation is based on a compilation technique that translates SQL/TP queries to SQL/92. In this way existing database systems can be used for managing temporal data. We substantiate this claim by proposing an experimental version of a SQL/TP compiler to serve as a front-end for DB2 1 13].