Nicolas Markey

Temporal logic with forgettable past

We investigate NLTL, a linear-time temporal logic with forgettable past. NLTL can be exponentially more succinct than LTL+Past (which in turn can be more succinct than LTL). We study satisfiability and model checking for NLTL and provide optimal automata-theoretic algorithms for these EXPSPACE-complete problems.

Infinite Runs in Weighted Timed Automata with Energy Constraints

We study the problems of existence and construction of infinite schedules for finite weighted automata and one-clock weighted timed automata, subject to boundary constraints on the accumulated weight. More specifically, we consider automata equipped with positive and negative weights on transitions and locations, corresponding to the production and consumption of some resource (e.g.energy). We ask the question whether there exists an infinite path for which the accumulated weight for any finite prefix satisfies certain constraints (e.g.remains between 0 and some given upper-bound). We also consider a game version of the above, where certain transitions may be uncontrollable.

Improved undecidability results on weighted timed automata

A focused crawler is designed to traverse the Web to gather documents on a specific topic. It can be used to build domain-specific Web search portals and online personalized search tools. To estimate the relevance of a newly seen URL, it must use information gleaned from previously crawled page sequences.In this paper, we present a new approach for prediction of the links leading to relevant pages based on a Hidden Markov Model (HMM). The system consists of three stages: user data collection, user modelling via sequential pattern learning, and focused crawling. In particular, we first collect the Web pages visited during a user browsing session. These pages are clustered, and the link structure among pages from different clusters is then used to learn page sequences that are likely to lead to target pages. The learning is performed using HMM. During crawling, the priority of links to follow is based on a learned estimate of how likely the page is to lead to a target page. We compare the performance with Context-Graph crawling and Best-First crawling. Our experiments demonstrate that this approach performs better than Context-Graph crawling and Best-First crawling.

Model Checking Timed Automata with One or Two Clocks

In this paper, we study model checking of timed automata (TAs), and more precisely we aim at finding efficient model checking for subclasses of TAs. For this, we consider model checking TCTL and TCTL ≤,≥ over TAs with one clock or two clocks.

On the expressiveness of TPTL and MTL

Abstract TPTL and MTL are two classical timed extensions of LTL . In this paper, we prove the 20-year-old conjecture that TPTL is strictly more expressive than MTL . But we show that, surprisingly, the TPTL formula proposed by Alur and Henzinger for witnessing this conjecture it can be expressed in MTL . More generally, we show that TPTL formulae using only modality F can be translated into MTL .

Model Checking a Path

We consider the problem of checking whether a finite (or ultimately periodic) run satisfies a temporal logic formula. This problem is at the heart of “runtime verification” but it also appears in many other situations. By considering several extended temporal logics, we show that the problem of model checking a path can usually be solved efficiently, and profit from specialized algorithms. We further show it is possible to efficiently check paths given in compressed form.

Robustness and Implementability of Timed Automata

In a former paper, we defined a new semantics for timed automata, the Almost ASAP semantics, which is parameterized by Δ to cope with the reaction delay of the controller. We showed that this semantics is implementable provided there exists a strictly positive value for the parameter Δ for which the strategy is correct. In this paper, we define the implementability problem to be the question of existence of such a Δ. We show that this question is closely related to a notion of robustness for timed automata defined in [Pur98] and prove that the implementability problem is decidable.

ATL with Strategy Contexts: Expressiveness and Model Checking

We study the alternating-time temporal logics ATL and ATL* extended with strategy contexts: these make agents commit to their strategies during the evaluation of formulas, contrary to plain ATL and ATL* where strategy quantifiers reset previously selected strategies. We illustrate the important expressive power of strategy contexts by proving that they make the extended logics, namely ATLsc and ATLsc*, equally expressive: any formula in ATLsc* can be translated into an equivalent, linear-size ATLsc formula. Despite the high expressiveness of these logics, we~prove that their model-checking problems remain decidable by~designing a tree-automata-based algorithm for model-checking ATLsc* on the full class of

Quantitative analysis of real-time systems using priced timed automata

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Model-Checking One-Clock Priced Timed Automata

-player concurrent game structures.