Contract Embeddings for Layered Control Architectures

The design of complex cyber-physical system architectures is often hierarchical. System specifications are mapped to an implementation layer via a stepwise refinement process involving multiple intermediate layers. These layers may capture different functionalities, and the orchestration of a variety of heterogeneous techniques suited to each layer may be required to achieve the overall design objectives. Due to their heterogeneity, ensuring traceability and verifiability of such architectures is a challenging problem. In this paper, we present a correct-by-construction methodology for designing heterogeneous layered architectures. We capture the specifications at each layer with assume-guarantee contracts , a specification paradigm which can encompass a variety of modeling formalisms. We then use the notion of contract embeddings to define specification refinement , rigorously and traceably mapping specifications across layers modeled with heterogeneous formalisms. We instantiate our methodology on the design of layered control architectures (LCAs), resulting in a novel approach that can verifiably orchestrate domain-specific techniques to satisfy both global planning and local safety requirements. In the context of LCAs, we derive necessary conditions for correct specification refinement and results for compositional realization of control safety specifications. We illustrate our design methodology on a motivating example and a case study derived from robotic mission planning and control.