An approach for persistent time-varying values

Abstract

As reactive systems, such as cyber-physical systems and the Internet of Things, become increasingly important, time-varying values, also known as signals, are playing an important role in software development. Although reactive systems require the change histories of some signals to be stored for various purposes such as post analysis and simulation, current programming languages do not provide a way to declare that signals are persistent. This paper proposes a method that realizes persistent signals in a reactive programming language, where (1) every update to each persistent signal is recorded in a time-series database, which can be seen as a part of the programming language runtime; and (2) persistent signals support a convenient time-oriented query mechanism. In this approach, each signal in the reactive programming language is seamlessly connected with the time-series database. This method is implemented as an extension of SignalJ, a Java-based reactive programming language that supports signals. In the implementation, the persistent signal mechanism is integrated with TimescaleDB, a PostgreSQL-based time-series database. In preliminary performance evaluations, our implementation had good responsiveness on most tests, indicating its feasibility for use in many applications.