On query optimization in a temporal SPC algebra

Abstract

Tuples of a temporal relation are equipped with a valid time period. A simple extension of the selection–projection–cross product (SPC) algebra for temporal relations is defined, which conforms to primitives in existing temporal query languages. In particular, temporal projection involves coalescing of time intervals, which results in non-monotonic queries. Also the “select-from-where” normal form is no longer available in this temporal extension. In view of these temporal peculiarities, it is natural and significant to ask whether query optimization techniques for the SPC algebra still apply in the temporal case. To this extent, we provide a temporal extension of the classical tableau formalism, and show its use and limits for temporal query optimization.