Reducing the number of clock variables of timed automata

Abstract. This paper attempts to improve our understanding of timed languages and their relation to timed automata. We start by giving a constructive proof of the folk theorem stating that timed languages specified by the past fragment of MITL, can be accepted by deterministic timed automata. On the other hand we provide a proof that certain languages expressed in the future fragment of MITL are not deterministic, 4 and analyze the reason for this asymmetry.

Section: Acceptance Conditionsmentioning

confidence: 99%

Real Time Temporal Logic: Past, Present, Future

Maler

Ničković

Pnueli

2005

“…The data under the title "No partial order" were obtained by our implementation setting all transitions dependent. They are results in principle in the same basic algorithm used by UppAal, but our implementation is lacking abstraction techniques like [8], which explains the largely superior results obtained by UppAal. The potential of the reduction can thus be seen by comparing the figures with and without "partial order" reduction.…”

Section: Experiments and Conclusionmentioning

confidence: 99%

“…Despite the theoretical limits (for a PSPACE complete problem), great effort has been invested into the optimization of the symbolic approach (see e.g. [8,4,7,2]). …”

Section: Introductionmentioning

confidence: 99%

Adding Invariants to Event Zone Automata

Niebert

2006

Abstract. Recently, a new approach to the symbolic model checking of timed automata based on a partial order semantics was introduced, which relies on event zones that use vectors of event occurrences instead of clock zones that use vectors of clock values grouped in polyhedral clock constraints. Symbolic state exploration with event zones rather than clock zones can result in significant reductions in the number of symbolic states explored. In this work, we show how to extend the event zone approach to networks of automata with local state invariants, an important feature for modeling complex timed systems. To avoid formalizing local states, we attach to each transition an urgency constraint, that allows to code local state invariants. We have integrated the extension into a prototype tool with event zones and reported very promising experimental results.

“…Finally we could also restrict the removal of the two previous methods to the active diagonal constraints in the current control location, following the idea proposed for clocks by Daws and Yovine in [DY96], and generalized in [BBFL03]. Note that all these methods induce a complexity blow-up even if there is no falsepositive execution.…”

Section: Systematic Removal Of Diagonal Constraintsmentioning

confidence: 99%

Diagonal Constraints in Timed Automata: Forward Analysis of Timed Systems

Bouyer

Laroussinie

Reynier

2005

Abstract. Timed automata (TA) are a widely used model for real-time systems. Several tools are dedicated to this model, and they mostly implement a forward analysis for checking reachability properties. Though diagonal constraints do not add expressive power to classical TA, the standard forward analysis algorithm is not correct for this model. In this paper we survey several approaches to handle diagonal constraints and propose a refinement-based method for patching the usual algorithm: erroneous traces found by the classical algorithm are analyzed, and used for refining the model.