Probabilistic Model-Based Safety Analysis

Model-based safety analysis approaches aim at finding critical failure combinations by analysis of models of the whole system (i.e. software, hardware, failure modes and environment). The advantage of these methods compared to traditional approaches is that the analysis of the whole system gives more precise results. Only few model-based approaches have been applied to answer quantitative questions in safety analysis, often limited to analysis of specific failure propagation models, limited types of failure modes or without system dynamics and behavior, as direct quantitative analysis is uses large amounts of computing resources. New achievements in the domain of (probabilistic) model-checking now allow for overcoming this problem. This paper shows how functional models based on synchronous parallel semantics, which can be used for system design, implementation and qualitative safety analysis, can be directly re-used for (model-based) quantitative safety analysis. Accurate modeling of different types of probabilistic failure occurrence is shown as well as accurate interpretation of the results of the analysis. This allows for reliable and expressive assessment of the safety of a system in early design stages

Model exploration and analysis for quantitative safety refinement in probabilistic B

The role played by counterexamples in standard system analysis is well known; but less common is a notion of counterexample in probabilistic systems refinement. In this paper we extend previous work using counterexamples to inductive invariant properties of probabilistic systems, demonstrating how they can be used to extend the technique of bounded model checking-style analysis for the refinement of quantitative safety specifications in the probabilistic B language. In particular, we show how the method can be adapted to cope with refinements incorporating probabilistic loops. Finally, we demonstrate the technique on pB models summarising a one-step refinement of a randomised algorithm for finding the minimum cut of undirected graphs, and that for the dependability analysis of a controller design.Comment: In Proceedings Refine 2011, arXiv:1106.348

Tutoring Multilingual Students: Shattering the Myths

This is the author's accepted manuscript, made available 18 months after publication with the permission of the publisher.The increasing linguistic and cultural diversification of North America has resulted in large numbers of multilingual students attending college and university and seeking curricular and extracurricular support with reading and writing (Ruecker, 2011; Teranishi, C. Suárez-Orozco, & M. Suárez-Orozco, 2011). In the past, learning and writing centers hired “ESL specialists” to provide support. But this model, given the ubiquity of multilingual students in higher education today, is no longer sustainable. Instead, all tutors must learn the skills necessary to support the academic literacy development of these writers, and that means that the way tutors are trained must change. Because the lived reality of the majority of tutors (and center administrators) is monolingual (Bailey, 2012; Barron & Grimm, 2002), examining the myths generally held about multilingual students is essential to both our development as tutors and the development of our students as academic readers and writers of English. Only after raising critical awareness about these “misguided ideas” will training specific to tutoring multilingual students make sense and be put into practice (Gillespie & Lerner, 2008, p. 117). In this article, I present and challenge myths about multilingual writers and myths about how to tutor them

RiskStructures : A Design Algebra for Risk-Aware Machines

Machines, such as mobile robots and delivery drones, incorporate controllers responsible for a task while handling risk (e.g. anticipating and mitigating hazards; and preventing and alleviating accidents). We refer to machines with this capability as risk-aware machines. Risk awareness includes robustness and resilience, and complicates monitoring (i.e., introspection, sensing, prediction), decision making, and control. From an engineering perspective, risk awareness adds a range of dependability requirements to system assurance. Such assurance mandates a correct-by-construction approach to controller design, based on mathematical theory. We introduce RiskStructures, an algebraic framework for risk modelling intended to support the design of safety controllers for risk-aware machines. Using the concept of a risk factor as a modelling primitive, this framework provides facilities to construct, examine, and assure these controllers. We prove desirable algebraic properties of these facilities, and demonstrate their applicability by using them to specify key aspects of safety controllers for risk-aware automated driving and collaborative robots

An approach to semi-automatically determine mechanical hazards in VR models

A risk assessment is typically required by legal regulations in production automation. These regulations vary from country to country. Risk assessment is often incomplete in industrial practice. Not all hazards are detected and risks are estimated insufficiently. Furthermore, risks are mostly assessed after the design of the product and/or production process. As result additional safety measures to reduce risks will cause higher costs and delays. This paper proposes an approach to semi-automatically derive risk from a virtual reality (VR) model of a machine. The focus is on the specific category of crushing hazard. These include situations where a human being might be hurt by being crushed. The VR model is based on a CAD model which mostly has been developed during the design phase of almost all technical products. The core idea is to identify moving parts of the machine and to calculate possible crushing zones by automatic distance approximations. The used algorithm relies on geometric CAD data. It uses axis aligned bounding volumes (AABB's) and the octree data structure. The concept is implemented in a prototype which especially determines crushing and shearing hazards and visualizes the result in the VR model for the experts. The software supports the process of risk assessment a precise and methodical approach and hardly minimizes the possibility of non-considering potential safety hazards. The prototype permits an effective, exact and methodical practice to the experts responsible in the process of the risk assessment by giving targeted advices. Furthermore, it allows the analysis of crushing hazards already during the design phase

Embedding CTL* in an Extension to Interval Temporal Logic (ITL)

In this paper we present an embedding of the most common branching time logics (CTL/CTL∗) in an extension of interval temporal logic (ITL+). The significance of this result is threefold: first the theoretical aspect is, that branching time and linear time are not so much different. A more practical aspect is that the intuitive interactive proof method of symbolic execution of ITL+ can be used for branching time logics as well. The opposite direction is interesting as well, for a subset of finite state systems, interactive verification of ITL+ formulas can be translated into a model checking problem. The proof presented in this paper has been done with the interactive theorem prover KIV. So this contribution can also be seen as a case study on reasoning about temporal logics in an interactive verification environment

From discrete event simulation to virtual reality environments

Today's technical systems are often very complex. System dynamics are often hard to predict for humans. However, understanding system behavior is crucial for evaluating design variants and finding errors. One way to cope with this problem is to build logical or virtual simulations. Logical simulations are often very abstract, but can simulate complex behavioral sequences. Virtual reality (VR) simulation is very good for experiencing the system in a view close to reality. However, it is very often static or has only limited dynamics. Until now both approaches exist in relative isolation. In this paper, we report on our experiences in building a mixed simulation, here a discrete event simulator (DES) is coupled with a virtual reality (VR) environment. We will focus on technical and conceptual challenges, but also present possible use cases for user interaction in this strategy to make more detailed investigations possible. Finally a prototype based on the simulation tool "SLX" and the virtual reality environment "Virtual Development and Training Platform" is used to evaluate the approach