Query plans for conventional and temporal queries involving duplicates and ordering

Most real-world database applications contain a substantial portion of time references, or temporal data. Recent advances in temporal query languages show that such database applications could benefit substantially from built-in temporal support in the DBMS. To achieve this, temporal query representation, optimization and processing mechanisms must be provided. This paper presents a general algebraic foundation for query optimization that integrates conventional and temporal query optimization and is suitable for providing temporal support both via a stand-alone temporal DBMS and via a layer on top of a conventional DBMS. By capturing duplicate removal and retention and order preservation for all queries, as well as coalescence for temporal queries, this foundation formalizes and generalizes existing approaches