ABSTRACT
This chapter is about the layers of abstraction required to design and run digital twins (DTs) as part of cyber-physical systems (CPS). Accurate modeling of CPS is a multi-faceted task, even with model-based decomposition techniques. CPS are complex adaptive systems, which lead to design and engineering challenges of synchronizing DTs with their physical counterparts. Synchronization is commonly mitigated by component abstraction and communication mechanisms. However, abstractions can be made at varying levels of granularity. If the granularity is too fine, the DT model grows too large to be suitable for further composition. If the granularity is too coarse, the model is insufficient for refinement to meet operational CPS requirements. Hence, we propose a layered approach to DT modeling that facilitates working with coarse-grained abstractions in composing a CPS, while retaining the controllability of a CPS for operational purposes. Our approach takes a fine-grained abstraction and processes it to a coarser abstraction, in which each component is only offered actions that meet the respective logic in the abstraction. We exemplify a transportation case to demonstrate how the resulting architecture helps to find a proper balance between precision and controllability of CPS development and operation.
