Optimizing decomposition of software architecture for local recovery

Cataloged from PDF version of article.The increasing size and complexity of software systems has led to an amplified number of potential failures and as such makes it harder to ensure software reliability. Since it is usually hard to prevent all the failures, fault tolerance techniques have become more important. An essential element of fault tolerance is the recovery from failures. Local recovery is an effective approach whereby only the erroneous parts of the system are recovered while the other parts remain available. For achieving local recovery, the architecture needs to be decomposed into separate units that can be recovered in isolation. Usually, there are many different alternative ways to decompose the system into recoverable units. It appears that each of these decomposition alternatives performs differently with respect to availability and performance metrics. We propose a systematic approach dedicated to optimizing the decomposition of software architecture for local recovery. The approach provides systematic guidelines to depict the design space of the possible decomposition alternatives, to reduce the design space with respect to domain and stakeholder constraints and to balance the feasible alternatives with respect to availability and performance. The approach is supported by an integrated set of tools and illustrated for the open-source MPlayer software

Two-scale EHL: three-dimensional topography in tilted-pad bearings

Derived from the Heterogeneous Multiscale Methods (HMM), a two-scale method is developed for the analysis of Elastohydrodynamic Lubrication (EHL) and micro-EHL in tilted-pad bearings with three-dimensional topography. A relationship linking the pressure gradient to mass flow rate is derived and represented in the bearing domain through homogenisation of near-periodic simulations describing the Fluid Structure Interaction (FSI) of topographical features. For the parameters investigated the influence of compressibility and piezoviscosity was found to be more significant than that of non-Newtonian (shear-thinning) behaviour on textured bearing performance. As the size of topography increased two-scale solutions demonstrated that at constant load the coefficient of friction increased and the minimum film thickness decreased over a range of pad lengths and tilt angles

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Peer reviewe

Safety Case Driven Development for Medical Devices

Medical devices are safety-critical systems that must comply with standards during their development process because of their intrinsic potential of producing harms. Although the existing trend of an increasing complexity of medical hardware and software components, very little has been done in order to apply more mature safety practices already present on other industrial scenarios. This paper proposes a methodology to enhance the Model-Based System Engineering (MBSE) state-of-art practices from the safety perspective, encouraging the use of safety cases and providing guidance on how to show the correspondent traceability for the development artifacts. We illustrate our methodology and its usage in the context of an industrial Automated External Defibrillator (AED). We suggest that medical device industry could learn from other domains and adapt its development to take into account the hazards and risks along the development, providing more sophisticated justification, as, for example, the impact of design decisions

Continuous rearchitecting of QoS models: Collaborative analysis for uncertainty reduction

Architecting high quality software systems is not trivial, in fact to know whether a certain quality attribute has been achieved, it has to be continuously analysed. Reasoning about multiple quality attributes (e.g., performance, availability) of software systems is even more difficult since it is necessary to jointly analyze multiple and heterogeneous Quality-of-Service (QoS) models. The goal of this paper is to investigate the combined use of different QoS models and continuously re-architecting them since the acquired knowledge of a specific QoS model may affect another model, thus to put in place a collaborative analysis process that reduces the overall uncertainty. Starting from an example of interaction among two different QoS models, i.e., a Bayesian Network for availability and a Queueing Network for performance, we demonstrate that the collaborative analysis brings benefits to the overall process since the initial uncertainty is reduced. We identify the join/fork points within the analysis process to bring upfront the quality characteristics of software systems, thus to enable the rearchitecting of systems in case of quality flaws. In this way, the QoS analysis becomes an integrated activity in the whole software development life-cycle and quality characteristics are continuously exposed to system architects