ST-DEVS: A Methodology Using Time-Dependent-Variable-Based Spatiotemporal Computation

Abstract

Various real systems are being replicated in cyberspace to solve complex and difficult problems, as exemplified by the digital twin. Once such a software system is implemented, an effective computational method should be applied to the system so that the corresponding real system, connected by networks or sensors, can be indirectly controlled. Considering that all behaviors in real systems occur in space−time, the behavior-related computation in the corresponding software system should adopt both time and space as essential elements to ensure a valid representation of the real system and to effectively perform subsequent computations. Therefore, applying a spatiotemporal computation consisting of time-dependent variables and temporal statements that use such variables is a natural approach to solving problems encountered in the target real system. In this study, the ST-DEVS (spatiotemporal computation DEVS) formalism is proposed to define time-dependent variables and an execution algorithm on temporal logic statements whose arguments are the time-dependent variables; the ST-DEVS is an extension of the discrete event system specification (DEVS). To control real systems with a certain level of autonomy, at least two basic capabilities must be ensured: monitoring and action execution. In this study, action-type temporal logic with time-dependent variables and an action execution algorithm are proposed to illustrate the effectiveness of the spatiotemporal computation process. The previously defined monitoring capability is integrated into ST-DEVS so that monitoring and action execution can be processed uniformly. The proposed approach is designed considering the symmetry between the real world and the cyber world, in that both worlds are influenced by time and space.