Showing papers by "Christian Schallhart published in 2006"

Monitoring of real-time properties

Abstract: This paper presents a construction for runtime monitors that check real-time properties expressed in timed LTL (TLTL). Due to D'Souza's results, TLTL can be considered a natural extension of LTL towards real-time. Moreover, a typical obstacle in runtime verification is solved both for untimed and timed formulae, in that standard models of linear temporal logic are infinite traces, whereas in runtime verification only finite system behaviours are at hand. Therefore, a 3-valued semantics (true, false, inconclusive) for LTL and TLTL on finite traces is defined that resembles the infinite trace semantics in a suitable and intuitive manner. Then, the paper describes how to construct, given a (T)LTL formula, a deterministic monitor with three output symbols that reads a finite trace and yields its according 3-valued (T)LTL semantics. Notably, the monitor rejects a trace as early as possible, in that any minimal bad prefix results in false as a return value.

Model-based runtime analysis of distributed reactive systems

Abstract: Reactive distributed systems have pervaded everyday life and objects, but often lack measures to ensure adequate behaviour in the presence of unforeseen events or even errors at runtime. As interactions and dependencies within distributed systems increase, the problem of detecting failures which depend on the exact situation and environment conditions they occur in grows. As a result, not only the detection of failures is increasingly difficult, but also the differentiation between the symptoms of a fault, and the actual fault itself, i.e., the cause of a problem. In this paper, we present a novel and efficient approach for analysing reactive distributed systems at runtime, in that we provide a framework for detecting failures as well as identifying their causes. Our approach is based upon monitoring safety-properties, specified in the linear time temporal logic LTL (respectively, TLTL) to automatically generate monitor components which detect violations of these properties. Based on the results of the monitors, a dedicated diagnosis is then performed in order to identify explanations for the misbehaviour of a system. These may be used to store detailed log files, or to trigger recovery measures. Our framework is built modular, layered, and uses merely a minimal communication overhead - especially when compared to other, similar approaches. Further, we sketch first experimental results from our implementations, and describe how it can be used to build a variety of distributed systems using our techniques.

Runtime Reflection: Dynamic model-based analyis of component-based distributed embedded systems

Abstract: Distributed embedded systems have pervaded the automotive domain, but often still lack measures to ensure adequate behaviour in the presence of unforeseen events, or even errors at runtime. As interactions and dependencies within distributed automotive systems increase, the problem of detecting failures which depend on the exact situation and environment conditions they occur in grows. As a result, not only the detection of failures is increasingly difficult, but also the differentiation between the symptoms of a fault, and the actual fault itself, i. e., the cause of a problem. In this paper, we present a novel and efficient approach built around the notion of a software component similar to AUTOSAR, for dynamically analysing distributed embedded systems in the testing phase or even in standard operation, in that we provide a framework for detecting failures as well as identifying their causes. Our approach is based upon monitoring safety properties, specified in a language that allows to express dynamic system properties. For such specifications so-called monitor components are generated automatically to detect violations of software components. Based on the results of the monitors, a dedicated diagnosis is then performed in order to identify explanations for the misbehaviour of a system. These may be used to store detailed error logs, or to trigger recovery measures.

Monitoring of real-time properties

Abstract: This paper presents a construction for runtime monitors that check real-time properties expressed in timed LTL (TLTL). Due to D'Souza's results, TLTL can be considered a natural extension of LTL towards real-time. Moreover, a typical obstacle in runtime verification is solved both for untimed and timed formulae, in that standard models of linear temporal logic are infinite traces, whereas in runtime verification only finite system behaviours are at hand. Therefore, a 3-valued semantics (true, false, inconclusive) for LTL and TLTL on finite traces is defined that resembles the infinite trace semantics in a suitable and intuitive manner. Then, the paper describes how to construct, given a (T)LTL formula, a deterministic monitor with three output symbols that reads a finite trace and yields its according 3-valued (T)LTL semantics. Notably, the monitor rejects a trace as early as possible, in that any minimal bad prefix results in false as a return value.

Sat7 - Engineering a Modular SAT-Solver

Abstract: As many other SAT-solvers are developed in an artful but monolithic style, we took interest in the question whether it is possible to design and implement a modular SAT-solver in a well-engineered and modular way. In particular, we are developing a framework which allows to exchange and adapt various components of the overall SAT-solver in order to match the requirements of particular problem instances. The analysis and copy-implementation of a preexisting and successful SATsolver was a natural starting point for our project. We chose minisat 1.14 [1] as guiding example, since minisat is an award-winning, yet compact solver. The reengineering of minisat resulted in an algorithmically equivalent solver which is decomposed into a number of orthogonal and exchangeable components. In the process of analyzing minisat and developing its equivalent but modular sibling, minisat7, we found a number of approaches for potential improvements. Thus, once minisat7 was running twice as long as minisat in the worst case, we started a branch from the faithful copy in order to develop our own solver Sat7. However, due to the lack of time, we were unable to pursue the implementation and testing of most of our ideas. Consequently, we submit Sat7, a variant of minisat which is