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Assurance Aware Contract-Based Design for Safety-Critical Systems



Publication Type:

Doctoral Thesis


Safety-critical systems usually need to comply with a domain-specific safety standard, which often require a safety case in form of an explained argument supported by evidence to show that the system is acceptably safe to operate in a given context. Developing such a safety case is a time-consuming and costly process. Contact-based design has the potential to reduce the cost and time needed to develop both the system and the accompanying safety case. It supports systematic component reuse, and enables contract-based compositional verification of properties on a system model such that its results can be used as evidence in assuring that the system is acceptably safe. But while contract-based design focuses on reuse of component implementations and contract specifications, reuse of safety-relevant components in safety-critical systems needs to cover more than just the implementation. As many safety-relevant artefacts related to the component as possible should be reused together with the implementation to assist the integrator in assuring that the system they are developing is acceptably safe.In this thesis we focus on developing a notion of safety contracts that can be used to guide the assurance of a system as well as facilitate systematic reuse of safety-relevant components and their accompanying assurance artefacts. Such contracts aim at making the contract-based design aware of both assurance and reuse of safety-relevant artefacts. To make the contract-based design assurance-aware, we capture the reasoning for communicating the confidence in the system using contracts in form of safety argumentation patterns of reusable reasoning. Then, we define the variability on the contract level to facilitate capturing different behaviours that reusable components can exhibit in different contexts. We define a meta-model that connects such contract-based system modelling with assurance modelling to support reuse of assurance artefacts as well as to automate the instantiation of the contract-driven argumentation patterns. To support adoption of the proposed contract-based reuse and assurance, we explore how the contracts can be combined with the existing failure logic analyses, and align the contract-driven assurance and reuse approach with the notion of Safety Element out of Context proposed within the automotive functional safety standard ISO 26262. We provide tool support for contract-driven assurance and reuse within the AMASS tool platform and evaluate the tool-supported methodology in industrial case studies.


author = {Irfan Sljivo},
title = {Assurance Aware Contract-Based Design for Safety-Critical Systems},
month = {September},
year = {2018},
school = {M{\\"{a}}lardalen University},
url = {}