Modelling Time in Query Languages

In this paper, an approach to handle time in relational query languages is outlined. The approach is based on extending Boolean and Comparison operators by allowing their operands to be sets of intervals. Proposed model provides temporal retrieval capability using an extended logic for comparison and Boolean operators. The extended logic allows these operators to accept sets of intervals and return results in the form of sets of intervals. New syntax for retrieval statements is defined in order to separate the process of selecting entities (tuples) and the process of selecting required values of temporal attributes from the chosen entities. The extensions presented in this paper offer a good degree of flexibility in expressing different temporal requirements.