Databases and Temporal Constraints: Semantics and Complexity

Abstract

We continue the development of a theory of constraint databases with indefinite information which we originated in our previous research. Initially we review the schemes of ℒ-constraint databases and indefinite ℒ -constraint databases where ℒ, the parameter, is a first-order constraint language. Then we consider several instances of these schemes where ℒ is a language for expressing information about atomic data values and time. We collectively refer to these models as temporal constraint databases and indefinite temporal constraint databases. We give a detailed characterization of the computational complexity of query answering for various classes of temporal constraint databases and queries. Our results results are theoretical but can be summarized as follows for a wider database audience: The worst-case complexity of query evaluation does not change when we move from queries in relational calculus over relational databases, to queries in relational calculus with temporal constraints over temporal constraint databases. This fact remains true even if we consider indefinite relational databases vs. indefinite temporal constraint databases.