Enabling causality learning in smart factories with hierarchical digital twins

Smart factories are complex systems where many different components need to interact and cooperate in order to achieve common goals. In particular, devices must be endowed with the skill of learning how to react in front of evolving situations and unexpected scenarios. In order to develop these capabilities, we argue that systems will need to build an internal, and possibly shared, representation of their operational world that represents causal relations between actions and observed variables. Within this context, digital twins will play a crucial role, by providing the ideal infrastructure for the standardisation and digitisation of the whole industrial process, laying the groundwork for the high-level learning and inference processes. In this paper, we introduce a novel hierarchical architecture enabled by digital twins, that can be exploited to build logical abstractions of the overall system, and to learn causal models of the environment directly from data. We implement our vision through a case study of a simulated production process. Our results in that scenario show that Bayesian networks and intervention via do-calculus can be effectively exploited within the proposed architecture to learn interpretable models of the environment. Moreover, we evaluate how the use of digital twins has a strong impact on the reduction of the physical complexity perceived by external applications.