Extensions to SQL for Historical Databases

A historical database management system (HDBMS) is a high-level facility which provides timing information and automatically maintains history (i.e., past) data. It also provides facilities for time-related queries. One such HDBMS is described in this paper. Our HDBMS uses an extended relational data model with state-oriented, instead of cubic, conceptualization. Two types of historical relations, called state and event relations, are provided for modeling realworld objects. The popular query langauge SQL has been extended for definition, retrieval, and update of historical relations. The extended SQL, called HSQL, is a superset of SQL. We define a few primitive algebra operations for historical relations, and use them as a basis for extensions to SQL. By doing so, HSQL retains the elegant structural and algebraic framework of SQL. HSQL contains a few new clauses, many operations and built-in functions on time domain, and facilities for retrospective updates and time-rollback