Querying Clocked Databases

We propose a temporal extension of Datalog which can be used to model and query temporal databases with relations based on multiple clocks. The extension, called Clocked Temporal Datalog, is based on a clocked temporal logic in which each predicate and hence each formula can be assigned a separate clock. A Clocked Temporal Datalog program consists of three parts: (1) a clock definition, (2) a clock assignment, and (3) a program body. The clock definition specifies all the available clocks. The clock assignment assigns to each predicate defined in the program body a clock from the clock definition. The meaning of the program body naturally depends on the provided clock definition and assignment. Therefore a Clocked Temporal Datalog program models intensionally a clocked database in which each relation is defined over a clock. Programmable clock definitions are very flexible in specifying periodic as well as some nonperiodic clocks, and in specifying relationships between clocks on the fly.