Conditions of contracts for separating responsibilities in heterogeneous systems

Abstract

A general, compositional, and component-based contract theory is proposed for modeling and specifying heterogeneous systems, characterized by consisting of parts from different domains, e.g. software, electrical and mechanical. Given a contract consisting of assumptions and a guarantee, clearly separated conditions on a component and its environment are presented where the conditions ensure that the guarantee is fulfilled-a responsibility assigned to the component, given that the environment fulfills the assumptions. The conditions are applicable whenever it cannot be ensured that the sets of ports of components are partitioned into inputs and outputs, and hence fully support scenarios where components, characterized by both causal and acausal models, are to be integrated by solely relying on the information of a contract. An example of such a scenario of industrial relevance is explicitly considered, namely a scenario in a supply chain where the development of a component is outsourced. To facilitate the application of the theory in practice, necessary properties of contracts are also derived to serve as sanity checks of the conditions. Furthermore, based on a graph that represents a structuring of a hierarchy of contracts, sufficient conditions to achieve compositionality are presented.

Providing tool support for specifying safety-critical systems by enforcing syntactic contract conditions

“…However, the principles behind contracts can be traced back to early ideas on compositional [33,66] proof-methods [32,41,55]. In [6,68,76], the use of contracts is extended from formal specification of SW to serving as a central systems engineering philosophy to support the design of systems in general. The work in [73] incorporates the work in [6,68,76] and presents a contracts theory that introduces new concepts such as architecture.…”

“…This support is provided by applying the work in [6,68,73,75,76] that present a formal and general contracts [53] theory for modeling and specifying systems.…”

“…These tasks (I)-(IV) are also described in FuSa standards; however, the fact is that in contracts theory [6,68,73,75,76], these tasks are given formal semantics, i.e., interpretations in formal (mathematical) conditions. The present paper capitalizes on this fact by considering the support that can be provided for tasks (I)-(IV) by having a tool that evaluates these formal contract conditions.…”

“…Despite the fact that formal representations have several advantages over non-formal ones, formal languages are difficult to use by non-experts [23] and in industrial practice, 'overcoming the burden of formalization is a major challenge' [10]. Therefore, instead of focusing on enforcing all of the contract conditions in [6,68,73,75,76], the present paper instead identifies necessary conditions of the formal interpretations of tasks (I)-(IV) where these conditions can be evaluated even when requirements and architectures are not represented formally; in the following, such necessary conditions will be called syntactic contract conditions.…”

“…Section 1.1 provides an overview of the contributions and validation approach of the paper. Section 2 introduces relevant parts of the contracts theory in [6,68,73,75,76]. Section 3 identifies syntactic contract conditions of tasks (I)-(IV) in this contracts theory, and as the main contribution, shows how support can be provided for tasks (I)-(IV) by enforcing these syntactic contract conditions.…”