Gerd Behrmann

A Tutorial on UPPAAL

This is a tutorial paper on the tool Uppaal. Its goal is to be a short introduction on the flavor of timed automata implemented in the tool, to present its interface, and to explain how to use the tool. The contribution of the paper is to provide reference examples and modeling patterns.

UPPAAL 4.0

UPPAAL 4.0 is the result of over two and a half years of development and contains many new features, additions to the modeling language, performance improvements, enhancements and polish to the easy to use graphical user interface, and is accompanied by several open source libraries. The tool and libraries are available free of charge for academic, educational and evaluation purposes from http://www.uppaal.com/. We describe three of the new features: user defined functions, priorities and symmetry reduction

UPPAAL-Tiga: time for playing games!

In 2005 we proposed the first efficient on-the-fly algorithm for solving games based on timed game automata with respect to reachability and safety properties. The first prototype presented at that time has now matured to a fully integrated tool with dramatic improvements both in terms of performance and the availability of the extended input language of UPPAAL-4.0. The new tool can output strategies or let the user play against them both from the command line and from the graphical simulator that was completely re-designed.

Minimum-Cost Reachability for Priced Time Automata

This paper introduces the model of linearly priced timed automata as an extension of timed automata, with prices on both transitions and locations. For this model we consider the minimum-cost reachability problem: i.e. given a linearly priced timed automaton and a target state, determine the minimum cost of executions from the initial state to the target state. This problem generalizes the minimum-time reachability problem for ordinary timed automata. We prove decidability of this problem by offering an algorithmic solution, which is based on a combination of branch-and-bound techniques and a new notion of priced regions. The latter allows symbolic representation and manipulation of reachable states together with the cost of reaching them.

As Cheap as Possible: Efficient Cost-Optimal Reachability for Priced Timed Automata

In this paper we present an algorithm for efficiently computing optimal cost of reaching a goal state in the model of Linearly Priced Timed Automata (LPTA). The central contribution of this paper is a priced extension of so-called zones. This, together with a notion of facets of a zone, allows the entire machinery for symbolic reachability for timed automata in terms of zones to be lifted to cost-optimal reachability using priced zones. We report on experiments with a cost-optimizing extension of Uppaal on a number of examples.

Optimal scheduling using priced timed automata

This contribution reports on the considerable effort made recently towards extending and applying well-established timed automata technology to optimal scheduling and planning problems. The effort of the authors in this direction has to a large extent been carried out as part of the European projects VHS [20] and AMETIST [16] and are available in the recently released UPPAAL CORA [12], a variant of the real-time verification tool UPPAAL [18, 5] specialized for cost-optimal reachability for the extended model of so-called priced timed automata.

UPPAAL: now, next, and future

UPPAAL is a tool for modeling, simulation and verification of real-time systems, developed jointly by BRICS at Aalborg University and the Department of Computer Systems at Uppsala University. The tool is appropriate for systems that can be modeled as a collection of non-deterministic processes with finite control structure and real-valued clocks, communicating through channels or shared variables. Typical application areas include real-time controllers and communication protocols, in particular those where timing aspects are critical. This paper reports on the currently available version and summarizes developments during the last two years. We report on new directions that extends UPPAAL with cost-optimal exploration, parametric modeling, stop-watches, probablistic modeling, hierachical modeling, executable timed automata, and a hybrid automata animator. We also report on recent work to improve the efficiency of the tool. In particular, we outline Clock Difference Diagrams (CDDs), new compact representations of states, a distributed version of the tool, and application of dynamic partitioning. UPPAAL has been applied in a number of academic and industrial case studies. We describe a selection of the recent case studies.

UPPAAL - present and future

UPPAAL is a tool for modelling, simulation and verification of real-time systems, developed jointly by BRICS at Aalborg University and the Department of Computer Systems at Uppsala University. The tool is appropriate for systems that can be modelled as a collection of non-deterministic processes with finite control structure and real-valued clocks, communicating through channels or shared variables. Typical application areas include real-time controllers and communication protocols in particular, those where timing aspects are critical. In this paper, we review the status of the currently distributed version of the tool as well as facilities to be found in upcoming releases.

Lower and upper bounds in zone-based abstractions of timed automata

Timed automata have an infinite semantics. For verification purposes, one usually uses zone-based abstractions w.r.t. the maximal constants to which clocks of the timed automaton are compared. We show that by distinguishing maximal lower and upper bounds, significantly coarser abstractions can be obtained. We show soundness and completeness of the new abstractions w.r.t. reachability and demonstrate how information about lower and upper bounds can be used to optimise the algorithm for bringing a difference bound matrix into normal form. Finally, we experimentally demonstrate that the new techniques dramatically increase the scalability of the real-time model checker UPPAAL.

Efficient Timed Reachability Analysis Using Clock Difference Diagrams

One of the major problems in applying automatic verification tools to industrial-size systems is the excessive amount of memory required during the state-space exploration of a model. In the setting of real-time, this problem of state-explosion requires extra attention as information must be kept not only on the discrete control structure but also on the values of continuous clock variables. In this paper, we exploit Clock Difference Diagrams, CDDs, a BDD-like data-structure for representing and effectively manipulating certain nonconvex subsets of the Euclidean space, notably those encountered during verification of timed automata. A version of the real-time verification tool Uppaal using CDDs as a compact data-structure for storing explored symbolic states has been implemented. Our experimental results demonstrate significant spacesavings: for eight industrial examples, the savings are in average 42% with moderate increase in runtime. We further report on how the symbolic state-space exploration itself may be carried out using CDDs.