CHRONUS is a query system that supports temporal extensions to the Structured Query Language (SQL) for relational databases. Although the relational data model can store timestamped data and permits simple temporal-comparison operations, the relational model does not provide either a closed or complete algebra for manipulating temporal data. In this paper, we outline an algebra that maintains a consistent relational structure for temporal data and that allows the type of temporal queries needed for protocol- directed decision support. We also discuss how CHRONUS can translate between our temporal algebra and the relational algebra used for SQL queries. We have applied our system to the task of screening patients for clinical trials. Our results demonstrate that CHRONUS can sufficiently express all required temporal queries, and that the search time of such queries is similar to that of standard SQL.
