Contract-Based Hierarchical Modeling and Traceability of Heterogeneous Requirements

The design of complex mission-critical systems often follows a layered approach, which may lead to complicated, multilevel, multiviewpoint requirement hierarchies. This heterogeneity makes it challenging to guarantee the traceability of the requirements across levels of abstraction and, consequently, the satisfaction of the requirements by a system implementation, especially when requirements at different abstraction levels are expressed using different mathematical formalisms and modeling languages. In this article, we address this challenge by introducing heterogeneous hierarchical contract networks (HHCNs), a formal model based on a graph of assume-guarantee contracts, for capturing and analyzing heterogeneous requirement hierarchies. We formulate the requirement traceability validation problem in terms of contract refinement relations between nodes in an HHCN. We then define contract embeddings to enable reasoning about refinements across levels of abstraction in the HHCN that are expressed using heterogeneous formalisms. Contract embeddings leverage the notion of conservative approximation to rigorously map contracts across levels of abstraction while ensuring that refinement is preserved independently of the formalism to which the contracts are mapped. We illustrate their effectiveness on a case study motivated by a multiagent autonomous lunar rover mission.