System analysis and robustness

Software is increasingly embedded in a variety of physical contexts. This imposes new requirements on tools that support the design and analysis of systems. For instance, modeling embedded and cyberphysical systems needs to blend discrete mathematics, which is suitable for modeling digital components, with continuous mathematics, used for modeling physical components. This blending of continuous and discrete creates challenges that are absent when the discrete or the continuous setting are considered in isolation. We consider robustness, that is, the ability of an analysis of a model to cope with small amounts of imprecision in the model. Formally, we identify analyses with monotonic maps between complete lattices (a mathematical framework used for abstract interpretation and static analysis) and define robustness for monotonic maps between complete lattices of closed subsets of a metric space.</p

Prefix orders as a general model of dynamics

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Modeling an impact control strategy using HyPA

\u3cp\u3eWe analyze a control strategy for the pick-and-place module of a component mounting device.We use a combination of techniques from bondgraph-theory, systems theory, process algebra and differential algebra to achieve this, and we show how the hybrid process algebra HyPA aides us in combining these techniques and in using them on a common hybrid model of the device.\u3c/p\u3

Simulation-based performance analysis of a medical image-processing architecture

In this paper, we show a simulation method for performance prediction of medical image processing chains, based on the real-time calculus of [9]. In particular, we focus on estimating the latency and throughput of a given image processing chain and its distribution over hardware resources. The architectural level of abstraction of the real-time calculus approach makes our method flexible, so that different design decisions can be studied using similar models. The choice for simulation rather than the usual algebraic analysis of real-time calculus equations, gives us the possibility to include a number of performance relevant implementation details in our models for which analytical estimates are not available

Towards periodic budgeting in real-time calculus

In this report, we extend the real-time calculus model with a periodic budgeting mechanism known as deferrable service. Based on this extended model, we prove a schedulability theorem for a real-time task under a deferrable server. Using this theorem, we show by means of an example that existing schedulability analysis for real-time tasks under a deferrable server is pessimistic rather than exact

Open maps in concrete categories and branching bisimulation for prefix orders

\u3cp\u3eOpen maps, as introduced in concurrency theory by Joyal, Nielsen and Winskel, provide an abstract way to define functional bisimulations across a wide variety of models of computation (like labelled transition systems, event structures, etcetera). Furthermore, the existence of a span of open maps characterises the well-known relational definition of bisimulations found in the literature associated with these models of computation. However, in our working category of prefix orders (in which the objects represent the sets of executions generated by arbitrary dynamical systems) the open maps do not immediately result in functional bisimulations and the existence of a span of open maps does not result in an equivalence. This is rather surprising, since prefix orders are mere generalizations of (discrete) execution trees, for which the open map approach is known to work. After taking a closer look at the definition of open map, we show in this paper that the issue can be remedied by considering prefix orders as a concrete category and reinterpreting the definition of open-map in this light. As a bonus, the choice of a path-category on which the notion of open-map relies becomes a natural one, namely the subcategory of embeddings. While the existence of spans still does not result in an equivalence, it is shown that the existence of cospans does. In fact, we present a characterisation of the notion of branching bisimulation by van Glabbeek and Weijland which, to the best of our knowledge, was not studied in the framework of open maps before.\u3c/p\u3

Desynchronisability of (partial) closed loop systems

The task of implementing a supervisory controller is non-trivial, even though there are different theories that allow automatic synthesis of these controllers in the form of automata. One of the reasons for this discord is due to the asynchronous interaction between a plant and its controller in implementations, whereas the existing supervisory control theories assume synchronous interaction. As a consequence the implementation suffers from the so-called inexact synchronisation problem. In this paper we address the issue of inexact synchronisation in a process algebraic setting, by solving a more general problem of refinement. We construct an asynchronous closed loop system by introducing a communication medium in a given synchronous closed loop system. Our goal is to find sufficient conditions under which a synchronous closed loop system is branching bisimilar to its corresponding asynchronous closed loop system. Furthermore, we extend our results to a class of synchronous closed loop systems called partial synchronous closed loop systems, whose alphabet contains external actions of both the plant and its controller that do not result in interaction

Efficient reprogramming of sensor networks using incremental updates and data compression

Reprogramming is an important issue in wireless sensor networks. It enables users to extend or correct functionality of a sensor network after deployment, at a low cost. In this paper, we investigate two problems: improving the energy efficiency and improving the delay of reprogramming. As enabling technologies we use data compression and incremental updates. We analyze different algorithms for both approaches, as well as their combination, when applied to resource-constrained devices. All algorithms are ported to the Contiki embedded operating system, and profiled for different types of reprogramming. Our results show that there is a clear trade-off between performance and resource requirements. Either VCDIFF, or the combination of Lempel-Ziv-77 or FastLZ compression algorithms with BSDIFF for delta encoding, have the best overall performance compared to other compression algorithms

Stakeholder impact on the software architecture of intelligent transport systems implementations

\u3cp\u3eModern vehicles are equipped with a lot of hard-and software systems that all generate in-vehicle data. Application development could benefit from a generic data acquisition layer to create a healthy, transparent and ethical data sharing environment. This paper investigates which policies are necessary in order to create this environment to stimulate development of applications that require access to in-vehicle data.\u3c/p\u3