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Mario Gleirscher

Publications and source records attributed to Mario Gleirscher.

36 records · Page 2Linked to original sources
arXiv2020

Integration of Formal Proof into Unified Assurance Cases with Isabelle/SACM

Assurance cases are often required to certify critical systems. The use of formal methods in assurance can improve automation, increase confidence, and overcome errant reasoning. However, assurance cases can never be fully formalised, as the use of formal methods is contingent on models that are validated by informal processes. Consequently, assurance techniques should support both formal and informal artifacts, with explicated inferential links between them. In this paper, we contribute a formal machine-checked interactive language, called Isabelle/SACM, supporting the computer-assisted construction of assurance cases compliant with the OMG Structured Assurance Case Meta-Model. The use of Isabelle/SACM guarantees well-formedness, consistency, and traceability of assurance cases, and allows a tight integration of formal and informal evidence of various provenance. In particular, Isabelle brings a diverse range of automated verification techniques that can provide evidence. To validate our approach, we present a substantial case study based on the Tokeneer secure entry system benchmark. We embed its functional specification into Isabelle, verify its security requirements, and form a modular security case in Isabelle/SACM that combines the heterogeneous artifacts. We thus show that Isabelle is a suitable platform for critical systems assurance.

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arXiv2020

Formal Methods in Dependable Systems Engineering: A Survey of Professionals from Europe and North America

Context: Formal methods (FMs) have been around for a while, still being unclear how to leverage their benefits, overcome their challenges, and set new directions for their improvement towards a more successful transfer into practice. Objective: We study the use of formal methods in mission-critical software domains, examining industrial and academic views. Method: We perform a cross-sectional on-line survey. Results: Our results indicate an increased intent to apply FMs in industry, suggesting a positively perceived usefulness. But the results also indicate a negatively perceived ease of use. Scalability, skills, and education seem to be among the key challenges to support this intent. Conclusions: We present the largest study of this kind so far (N = 216), and our observations provide valuable insights, highlighting directions for future theoretical and empirical research of formal methods. Our findings are strongly coherent with earlier observations by Austin and Parkin (1993).

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arXiv2020

Challenges in the Safety-Security Co-Assurance of Collaborative Industrial Robots

The coordinated assurance of interrelated critical properties, such as system safety and cyber-security, is one of the toughest challenges in critical systems engineering. In this chapter, we summarise approaches to the coordinated assurance of safety and security. Then, we highlight the state of the art and recent challenges in human-robot collaboration in manufacturing both from a safety and security perspective. We conclude with a list of procedural and technological issues to be tackled in the coordinated assurance of collaborative industrial robots.

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arXiv2020

Safety Controller Synthesis for Collaborative Robots

In human-robot collaboration (HRC), software-based automatic safety controllers (ASCs) are used in various forms (e.g. shutdown mechanisms, emergency brakes, interlocks) to improve operational safety. Complex robotic tasks and increasingly close human-robot interaction pose new challenges to ASC developers and certification authorities. Key among these challenges is the need to assure the correctness of ASCs under reasonably weak assumptions. To address this need, we introduce and evaluate a tool-supported ASC synthesis method for HRC in manufacturing. Our ASC synthesis is: (i) informed by the manufacturing process, risk analysis, and regulations; (ii) formally verified against correctness criteria; and (iii) selected from a design space of feasible controllers according to a set of optimality criteria. The synthesised ASC can detect the occurrence of hazards, move the process into a safe state, and, in certain circumstances, return the process to an operational state from which it can resume its original task.

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arXiv2020

Towards Deductive Verification of Control Algorithms for Autonomous Marine Vehicles

The use of autonomous vehicles in real-world applications is often precluded by the difficulty of providing safety guarantees for their complex controllers. The simulation-based testing of these controllers cannot deliver sufficient safety guarantees, and the use of formal verification is very challenging due to the hybrid nature of the autonomous vehicles. Our work-in-progress paper introduces a formal verification approach that addresses this challenge by integrating the numerical computation of such a system (in GNU/Octave) with its hybrid system verification by means of a proof assistant (Isabelle). To show the effectiveness of our approach, we use it to verify differential invariants of an Autonomous Marine Vehicle with a controller switching between multiple modes.

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arXiv2019

New Opportunities for Integrated Formal Methods

Formal methods have provided approaches for investigating software engineering fundamentals and also have high potential to improve current practices in dependability assurance. In this article, we summarise known strengths and weaknesses of formal methods. From the perspective of the assurance of robots and autonomous systems (RAS), we highlight new opportunities for integrated formal methods and identify threats to the adoption of such methods. Based on these opportunities and threats, we develop an agenda for fundamental and empirical research on integrated formal methods and for successful transfer of validated research to RAS assurance. Furthermore, we outline our expectations on useful outcomes of such an agenda.

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arXiv2019

Mechanised Assurance Cases with Integrated Formal Methods in Isabelle

Assurance cases are often required as a means to certify a critical system. Use of formal methods in assurance can improve automation, and overcome problems with ambiguity, faulty reasoning, and inadequate evidentiary support. However, assurance cases can rarely be fully formalised, as the use of formal methods is contingent on models validated by informal processes. Consequently, we need assurance techniques that support both formal and informal artifacts, with explicated inferential links and assumptions that can be checked by evaluation. Our contribution is a mechanical framework for developing assurance cases with integrated formal methods based in the Isabelle system. We demonstrate an embedding of the Structured Assurance Case Meta-model (SACM) using Isabelle/DOF, and show how this can be linked to formal analysis techniques originating from our verification framework, Isabelle/UTP. We validate our approach by mechanising a fragment of the Tokeneer security case, with evidence supplied by formal verification.

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arXiv2019

Risk Structures: Towards Engineering Risk-aware Autonomous Systems

Inspired by widely-used techniques of causal modelling in risk, failure, and accident analysis, this work discusses a compositional framework for risk modelling. Risk models capture fragments of the space of risky events likely to occur when operating a machine in a given environment. Moreover, one can build such models into machines such as autonomous robots, to equip them with the ability of risk-aware perception, monitoring, decision making, and control. With the notion of a risk factor as the modelling primitive, the framework provides several means to construct and shape risk models. Relational and algebraic properties are investigated and proofs support the validity and consistency of these properties over the corresponding models. Several examples throughout the discussion illustrate the applicability of the concepts. Overall, this work focuses on the qualitative treatment of risk with the outlook of transferring these results to probabilistic refinements of the discussed framework.

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arXiv2019

Assurance of System Safety: A Survey of Design and Argument Patterns

The specification, design, and assurance of safety encompasses various concepts and best practices, subject of reuse in form of patterns. This work summarizes applied research on such concepts and practices with a focus on the last two decades and on the state-of-the-art of patterns in safety-critical system design and assurance argumentation. We investigate several aspects of such patterns, for example, where and when they are applied, their characteristics and purposes, and how they are related. For each aspect, we provide an overview of relevant studies and synthesize a taxonomy of first principles underlying these patterns. Furthermore, we comment on how these studies address known challenges and we discuss suggestions for further research. Our findings disclose a lack of research on how patterns improve system safety claims and, vice versa, on the decomposition of system safety into separated local concerns, and on the impact of security on safety.

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arXiv2018

Safety Practice and its Practitioners: Exploring a Diverse Profession

System safety refers to a diverse engineering discipline assessing and improving various aspects of safety in socio-technical systems and their software-intensive sub-systems. While system safety has been a vital area of applied research for many decades, its practice and practitioners seem empirically still not well studied. Beyond mainly anecdotal evidence (interviews, on-line discussions), incident reports, and surveys, we are missing open, large-scale, and long-term investigations that promote knowledge transfer and research validation. We explore means for work safety practitioners rely on, factors influencing their performance, and their perception of their role in the system life cycle. Along with that we examine observations from previous research. We build a construct of safety practice, collect data for this construct using an on-line survey, summarise and interpret the collected data, and investigate several hypotheses based on the previous observations. We analyse and present the responses of 124 practitioners in safety-critical system and software projects. Aside from other findings, our data suggests that safety decision making mainly depends on expert opinion and project memory, lacks evidence that safety is typically a cost-benefit question, does not exhibit the prejudice that formal methods are not beneficial, leaves it unclear as to whether or not standards and methods have become inadequate, and indicates that safety is not typically confused with reliability. Additionally, we contribute a research design directing towards explanatory empirical studies of safety practice. Empirical research of safety practice is still in an early stage, bearing the risk of undesirable mismatches of the state of the art and the state of practice. However, this situation offers great opportunities for research.

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arXiv2018

Proceedings 2nd International Workshop on Safe Control of Autonomous Vehicles

These are the proceedings of the Second International Workshop on Safe Control of Autonomous Vehicles, which took place on the 10th of April 2018 in Porto, Portugal as an affiliated workshop of CSPWeek. The task of this workshop is to identify open research problems, discuss recent achievements, bring together researchers in, e.g., control theory, adaptive systems, machine self-organization and autonomy, mobile intelligent robotics, transportation, traffic control, machine learning, software verification, and dependability and security engineering.

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arXiv2018

From Hazard Analysis to Hazard Mitigation Planning: The Automated Driving Case

Vehicle safety depends on (a) the range of identified hazards and (b) the operational situations for which mitigations of these hazards are acceptably decreasing risk. Moreover, with an increasing degree of autonomy, risk ownership is likely to increase for vendors towards regulatory certification. Hence, highly automated vehicles have to be equipped with verified controllers capable of reliably identifying and mitigating hazards in all possible operational situations. To this end, available methods for the design and verification of automated vehicle controllers have to be supported by models for hazard analysis and mitigation. In this paper, we describe (1) a framework for the analysis and design of planners (i.e., high-level controllers) capable of run-time hazard identification and mitigation, (2) an incremental algorithm for constructing planning models from hazard analysis, and (3) an exemplary application to the design of a fail-operational controller based on a given control system architecture. Our approach equips the safety engineer with concepts and steps to (2a) elaborate scenarios of endangerment and (2b) design operational strategies for mitigating such scenarios.

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arXiv2018

Arguing from Hazard Analysis in Safety Cases: A Modular Argument Pattern

We observed that safety arguments are prone to stay too abstract, e.g. solutions refer to large packages, argument strategies to complex reasoning steps, contexts and assumptions lack traceability. These issues can reduce the confidence we require of such arguments. In this paper, we investigate the construction of confident arguments from (i) hazard analysis (HA) results and (ii) the design of safety measures, i.e., both used for confidence evaluation. We present an argument pattern integrating three HA techniques, i.e., FTA, FMEA, and STPA, as well as the reactions on the results of these analyses, i.e., safety requirements and design increments. We provide an example of how our pattern can help in argument construction and discuss steps towards using our pattern in formal analysis and computer-assisted construction of safety cases.

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arXiv2017

Run-Time Risk Mitigation in Automated Vehicles: A Model for Studying Preparatory Steps

We assume that autonomous or highly automated driving (AD) will be accompanied by tough assurance obligations exceeding the requirements of even recent revisions of ISO 26262 or SOTIF. Hence, automotive control and safety engineers have to (i) comprehensively analyze the driving process and its control loop, (ii) identify relevant hazards stemming from this loop, (iii) establish feasible automated measures for the effective mitigation of these hazards or the alleviation of their consequences. By studying an example, this article investigates some achievements in the modeling for the steps (i), (ii), and (iii), amenable to formal verification of desired properties derived from potential assurance obligations such as the global existence of an effective mitigation strategy. In addition, the proposed approach is meant for step-wise refinement towards the automated synthesis of AD safety controllers implementing such properties.

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arXiv2016

On the Benefit of Automated Static Analysis for Small and Medium-Sized Software Enterprises

Today's small and medium-sized enterprises (SMEs) in the software industry are faced with major challenges. While having to work efficiently using limited resources they have to perform quality assurance on their code to avoid the risk of further effort for bug fixes or compensations. Automated static analysis can reduce this risk because it promises little effort for running an analysis. We report on our experience in analysing five projects from and with SMEs by three different static analysis techniques: code clone detection, bug pattern detection and architecture conformance analysis. We found that the effort that was needed to introduce those techniques was small (mostly below one person-hour), that we can detect diverse defects in production code and that the participating companies perceived the usefulness of the presented techniques as well as our analysis results high enough to include the techniques in their quality assurance.

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arXiv2016

Introduction of Static Quality Analysis in Small and Medium-Sized Software Enterprises: Experiences from Technology Transfer

Today, small and medium-sized enterprises (SMEs) in the software industry face major challenges. Their resource constraints require high efficiency in development. Furthermore, quality assurance (QA) measures need to be taken to mitigate the risk of additional, expensive effort for bug fixes or compensations. Automated static analysis (ASA) can reduce this risk because it promises low application effort. SMEs seem to take little advantage of this opportunity. Instead, they still mainly rely on the dynamic analysis approach of software testing. In this article, we report on our experiences from a technology transfer project. Our aim was to evaluate the results static analysis can provide for SMEs as well as the problems that occur when introducing and using static analysis in SMEs. We analysed five software projects from five collaborating SMEs using three different ASA techniques: code clone detection, bug pattern detection and architecture conformance analysis. Following the analysis, we applied a quality model to aggregate and evaluate the results. Our study shows that the effort required to introduce ASA techniques in SMEs is small (mostly below one person-hour each). Furthermore, we encountered only few technical problems. By means of the analyses, we could detect multiple defects in production code. The participating companies perceived the analysis results to be a helpful addition to their current QA and will include the analyses in their QA process. With the help of the Quamoco quality model, we could efficiently aggregate and rate static analysis results. However, we also encountered a partial mismatch with the opinions of the SMEs. We conclude, that ASA and quality models can be a valuable and affordable addition to the QA process of SMEs.

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arXiv2015

Model-based Hazard and Impact Analysis

Hazard and impact analysis is an indispensable task during the specification and development of safety-critical technical systems, and particularly of their software-intensive control parts. There is a lack of methods supporting an effective (reusable, automated) and integrated (cross-disciplinary) way to carry out such analyses. This report was motivated by an industrial project whose goal was to survey and propose methods and models for documentation and analysis of a system and its environment to support hazard and impact analysis as an important task of safety engineering and system development. We present and investigate three perspectives of how to properly encode safety-relevant domain knowledge for better reuse and automation, identify and assess all relevant hazards, as well as pre-process this information and make it easily accessible for reuse in other safety and systems engineering activities and, moreover, in similar engineering projects.

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