Specifying and Structuring Requirements on Cyber-Physical Systems using Contracts

A contract splits the responsibilities between a component and its environment into a guarantee that expresses an intended property under the responsibility of the component, given that the environment fulfills the assumptions. Building on recent works where contracts are proposed as a means to meet the challenges in the design of Cyber-Physical Systems (CPSs), a general contract framework is presented that supports the modelling of both individual components and architectures of CPS - at all levels of design, as well as the structuring and specification of requirements on the components using contracts. To facilitate the specification of requirements, constraints that restrict the portsover which a contract is expressed are introduced to serve as sanity checks that the component and the environment meet their respective responsibilities. Furthermore, a new graph, called a contract structure is introduced to support the structuring and tracing of requirements on a CPS using contracts. As a proof-of-concept, the framework is used to specify and structure safety requirements on an industrial system, as proposed by ISO 26262.QS 2015ESPRESS