15 research outputs found
The Power of Proofs: New Algorithms for Timed Automata Model Checking (with Appendix)
This paper presents the first model-checking algorithm for an expressive
modal mu-calculus over timed automata, , and reports performance results for an implementation.
This mu-calculus contains extended time-modality operators and can express all
of TCTL. Our algorithmic approach uses an "on-the-fly" strategy based on proof
search as a means of ensuring high performance for both positive and negative
answers to model-checking questions. In particular, a set of proof rules for
solving model-checking problems are given and proved sound and complete; we
encode our algorithm in these proof rules and model-check a property by
constructing a proof (or showing none exists) using these rules. One noteworthy
aspect of our technique is that we show that verification performance can be
improved with \emph{derived rules}, whose correctness can be inferred from the
more primitive rules on which they are based. In this paper, we give the basic
proof rules underlying our method, describe derived proof rules to improve
performance, and compare our implementation of this model checker to the UPPAAL
tool.Comment: This is the preprint of the FORMATS 2014 paper, but this is the full
version, containing the Appendix. The final publication is published from
Springer, and is available at
http://link.springer.com/chapter/10.1007%2F978-3-319-10512-3_9 on the
Springer webpag
Integrated Model-checking for the Design of Safe and Efficient Distributed Software Commissioning
International audienc
Towards a Unified Theory of Timed Automata
Timed automata are finite-state machines augmented with special clock variables that reflect the advancement of time. Able to both capture real-time behavior and be verified algorithmically (model-checked), timed automata are used to model real-time systems. These observations have led to the development of several timed-automata verification tools that have been successfully applied to the analysis of a number of different systems; however, the practical utility of timed automata is undermined by the theories underlying different tools differing in subtle but important ways. Since algorithmic results that hold for the variant used by one tool may not apply to another variant, this complicates the application of different tools to different models. The thesis of this dissertation is this: the theory of timed automata can be unified, and a practical unified approach to timed-automata model checking can be built around the paradigm of proof search.
First, this dissertation establishes the mutual expressivity of timed automata variants, thereby providing precise characterizations of when theoretical results of one variant apply to other variants. Second, it proves powerful expressive properties about different logics for timed behavior, and as a result, enlarges the set of verifiable properties. Third, it discusses an implementation of a verification tool for an expressive fixpoint-based logic, demonstrating an application of this newly developed theory. The tool is based on a proof-search paradigm; verifying timed automata involves constructing proofs using proof rules that enable verification problems to be translated into subproblems that must be solved. The tool's performance is optimized by using derived proof rules, thereby providing a theoretically sound basis for faster model checking. Last, this dissertation utilizes the proofs generated during verification to gain additional information about the vacuous satisfaction of certain formulae: whether the automaton satisfied a formula by never satisfying certain premises of that specification. This extra information is often obtained without significantly decreasing the verifier's performance
Formal modelling and analysis of broadcasting embedded control systems
PhD ThesisEmbedded systems are real-time, communicating systems, and the effective
modelling and analysis of these aspects of their behaviour is regarded as essential
for acquiring confidence in their correct operation. In practice, it is important
to minimise the burden of model construction and to automate the analysis,
if possible. Among the most promising techniques for real-time systems are
reachability analysis and model-checking of networks of timed automata. We
identify two obstacles to the application of these techniques to a large class of
distributed embedded systems: firstly, the language of timed automata is too
low-level for straightforward model construction, and secondly, the synchronous,
handshake communication mechanism of the timed automata model does not fit
well with the asynchronous, broadcast mechanism employed in many distributed
embedded systems. As a result, the task of model construction can be unduly
onerous.
This dissertation proposes an expressive language for the construction of
models of real-time, broadcasting control systems, and demonstrates how effi-
cient analysis techniques can be applied to them.
The dissertation is concerned in particular with the Controller Area Network
(CAN) protocol which is emerging as a de facto standard in the automotive
industry. An abstract formal model of CAN is developed. This model is adopted
as the communication primitive in a new language, bCANDLE, which includes
value passing, broadcast communication, message priorities and explicit time.
A high-level language, CANDLE, is introduced and its semantics defined by
translation to bCANDLE. We show how realistic CAN systems can be described
in CANDLE and how a timed transition model of a system can be extracted for
analysis. Finally, it is shown how efficient methods of analysis, such as 'on-the-
fly' and symbolic techniques, can be applied to these models. The dissertation
contributes to the practical application of formal methods within the domain
of broadcasting, embedded control systemsSchool of Computing and Mathematics at the University of Northumbri