We consider the synthesis problem on timed automata with Büchi objectives, where delay choices made by a controller are subjected to small perturbations. Usually, the controller needs to avoid punctual guards, such as testing the equality of a clock to a constant. In this work, we generalize to a robustness setting that allows for punctual transitions in the automaton to be taken by controller with no perturbation. In order to characterize cycles that resist perturbations in our setting, we introduce a new structural requirement on the reachability relation along an accepting cycle of the automaton. This property is formulated on the region abstraction, and generalizes the existing characterization of winning cycles in the absence of punctual guards. We show that the problem remains within PSPACE despite the presence of punctual guards.

We introduce a subclass of concurrent game structures (CGS) with imperfect information in which agents are endowed with private data-sharing capabilities. Importantly, our CGSs are such that it is still decidable to model-check these CGSs against a relevant fragment of ATL. These systems can be thought as a generalization of architectures allowing information forks, that is, cases where strategic abilities lead to certain agents outside a coalition privately sharing information with selected agents inside that coalition. Moreover, in our case, in the initial states of the system, we allow information forks from agents outside a given set \(A\) to agents inside this group \(A\) . For this reason, together with the fact that the communication in our models underpins a specialized form of broadcast, we call our formalism \(A\) -cast systems . To underline, the fragment of ATL for which we show the model-checking problem to be decidable over \(A\) -cast is a large and significant one; it expresses coalitions over agents in any subset of the set \(A\) . Indeed, as we show, our systems and this ATL fragments can encode security problems that are notoriously hard to express faithfully: terrorist-fraud attacks in identity schemes.

We show that a history-based variant of alternating bisimulation with imperfect information allows it to be related to a variant of Alternating-time Temporal Logic (ATL) with imperfect information by a full Hennessy-Milner theorem. The variant of ATL we consider has a common knowledge semantics, which requires that the uniform strategy available for a coalition to accomplish some goal must be common knowledge inside the coalition, while other semantic variants of ATL with imperfect information do not accomodate a Hennessy-Milner theorem. We also show that the existence of a history-based alternating bisimulation between two finite Concurrent Game Structures with imperfect information (iCGS) is undecidable.

International audience

Abstract EB3 is a specification language for information systems. The core of the EB3 language consists of process algebraic specifications describing the behaviour of the entities in a system, and attribute function definitions describing the entity attributes. The verification of EB3 specifications against temporal properties is of great interest to users of EB3 . In this paper, we propose a translation from EB3 to LOTOS NT (LNT for short), a value-passing concurrent language with classical process algebra features. Our translation ensures the one-to-one correspondence between states and transitions of the labelled transition systems corresponding to the EB3 and LNT specifications. We automated this translation with the EB32LNT tool, thus equipping the EB3 method with the functional verification features available in the CADP toolbox.

We give a discretization of behaviors of timed automata, in which timed languages are represented as sets of words containing action symbols, a clock tick symbol 1, and two delay symbols δ − (negative delay) and δ + (positive delay). Unlike the region construction, our discretization commutes with intersection. We show that discretizations of timed automata are, in general, context-sensitive languages over Σ ∪ {1, δ + , δ − }, and give a class of counter automata that accepts exactly the class of languages that are discretizations of timed automata, and show that its emptiness problem is decidable.

We show that propositional linear temporal logic with knowledge modalities but without common knowledge has an undecidable satisfiability problem when interpreted in a ‘concrete’ semantics with perfect recall or with perfect recall and synchrony.We then conclude that this concrete semantics is not axiomatizable in the semantics, based on local states.

We present TCTLK, a continuous-time variant of the Computational Tree Logic with knowledge operators, generalizing both TCTL, the continuous-time variant of CTL, and CTLK, the epistemic generalization of CTL.Formulas are interpreted over timed automata, with a synchronous and perfect recall semantics,and the observability relation requires one to specify what clocks are visible for an agent.We show that, in general, the model-checking problem for TCTLK is undecidable, even if formulas do not use any clocks --and hence CTLK has an undecidable model-checking problem when interpreted over timed automata.On the other hand, we show that, when each agent can see all clock values,model-checking becomes decidable.

We give an algorithmic calculus of the reachability relations on clock values defined by timed automata. Our approach is a modular one, by computing unions, compositions and reflexive-transitive closure (star) of "atomic" relations. The essential tool is a new representation technique for n-clock relations - the 2n-automata - and our strategy is to show the closure under union, composition and star of the class of 2n-automata that represent reachability relations in timed automata.