Satisfying temporal consistency constraints of real-time databases

Abstract

In addition to timing constraints, a real-time database has temporal consistency constraints for its temporal data. The temporal consistency constraints require the data to represent a state of the real-world that is up-to-date and also require data to represent past states of the real-world with values that are close in time. Factors, such as concurrency control, can cause transactions to miss their deadlines and data to become temporally inconsistent. Approximate query processing (AQP) has been proposed as a strategy to satisfy the timing constraints of real-time databases. Approximate answers are provided by AQP if it is not possible to produce an exact answer by a specified deadline. In this paper, we examine the temporal consistency of the data during traditional and AQP. Four metrics of temporal consistency are utilized to compare the age and dispersion of the data during traditional query processing (TQP) versus approximate query processing. Simulation results identify factors, such as the concurrency control algorithm, the number of transactions and the percentage of query transactions, that affect the temporal inconsistency of the data.