795 research outputs found
Dense Integer-Complete Synthesis for Bounded Parametric Timed Automata
Ensuring the correctness of critical real-time systems, involving concurrent
behaviors and timing requirements, is crucial. Timed automata extend
finite-state automata with clocks, compared in guards and invariants with
integer constants. Parametric timed automata (PTAs) extend timed automata with
timing parameters. Parameter synthesis aims at computing dense sets of
valuations for the timing parameters, guaranteeing a good behavior. However, in
most cases, the emptiness problem for reachability (i.e., whether the emptiness
of the parameter valuations set for which some location is reachable) is
undecidable for PTAs and, as a consequence, synthesis procedures do not
terminate in general, even for bounded parameters. In this paper, we introduce
a parametric extrapolation, that allows us to derive an underapproximation in
the form of linear constraints containing not only all the integer points
ensuring reachability, but also all the (non-necessarily integer) convex
combinations of these integer points, for general PTAs with a bounded parameter
domain. We also propose two further algorithms synthesizing parameter
valuations guaranteeing unavoidability, and preservation of the untimed
behavior w.r.t. a reference parameter valuation, respectively. Our algorithms
terminate and can output constraints arbitrarily close to the complete result.
We demonstrate their applicability and efficiency using the tool Rom\'eo on two
classical benchmarks.Comment: This is an extended version of the paper by the same authors
published in the proceedings of the 9th International Workshop on
Reachability Problems (RP 2015
LTL Parameter Synthesis of Parametric Timed Automata
The parameter synthesis problem for parametric timed automata is undecidable
in general even for very simple reachability properties. In this paper we
introduce restrictions on parameter valuations under which the parameter
synthesis problem is decidable for LTL properties. The investigated bounded
integer parameter synthesis problem could be solved using an explicit
enumeration of all possible parameter valuations. We propose an alternative
symbolic zone-based method for this problem which results in a faster
computation. Our technique extends the ideas of the automata-based approach to
LTL model checking of timed automata. To justify the usefulness of our
approach, we provide experimental evaluation and compare our method with
explicit enumeration technique.Comment: 23 pages, extended versio
IMITATOR II: A Tool for Solving the Good Parameters Problem in Timed Automata
We present here Imitator II, a new version of Imitator, a tool implementing
the "inverse method" for parametric timed automata: given a reference valuation
of the parameters, it synthesizes a constraint such that, for any valuation
satisfying this constraint, the system behaves the same as under the reference
valuation in terms of traces, i.e., alternating sequences of locations and
actions. Imitator II also implements the "behavioral cartography algorithm",
allowing us to solve the following good parameters problem: find a set of
valuations within a given bounded parametric domain for which the system
behaves well. We present new features and optimizations of the tool, and give
results of applications to various examples of asynchronous circuits and
communication protocols.Comment: In Proceedings INFINITY 2010, arXiv:1010.611
Language Emptiness of Continuous-Time Parametric Timed Automata
Parametric timed automata extend the standard timed automata with the
possibility to use parameters in the clock guards. In general, if the
parameters are real-valued, the problem of language emptiness of such automata
is undecidable even for various restricted subclasses. We thus focus on the
case where parameters are assumed to be integer-valued, while the time still
remains continuous. On the one hand, we show that the problem remains
undecidable for parametric timed automata with three clocks and one parameter.
On the other hand, for the case with arbitrary many clocks where only one of
these clocks is compared with (an arbitrary number of) parameters, we show that
the parametric language emptiness is decidable. The undecidability result
tightens the bounds of a previous result which assumed six parameters, while
the decidability result extends the existing approaches that deal with
discrete-time semantics only. To the best of our knowledge, this is the first
positive result in the case of continuous-time and unbounded integer
parameters, except for the rather simple case of single-clock automata
Modeling a distributed Heterogeneous Communication System using Parametric Timed Automata
In this report, we study the application of the Parametric Timed Automata(PTA) tool to a concrete case of a distributed Heterogeneous Communication System (HCS). The description and requirements of HCS are presented and the system modeling is explained carefully. The system models are developed in UPPAAL and validated by different test cases. Part of the system models are then converted into parametric timed automata and the schedulability checking is run to produce the schedulability regions
Classification-based parameter synthesis for parametric timed automata
National Research Foundation (NRF) Singapor
Configuring Timing Parameters to Ensure Execution-Time Opacity in Timed Automata
Timing information leakage occurs whenever an attacker successfully deduces
confidential internal information by observing some timed information such as
events with timestamps. Timed automata are an extension of finite-state
automata with a set of clocks evolving linearly and that can be tested or
reset, making this formalism able to reason on systems involving concurrency
and timing constraints. In this paper, we summarize a recent line of works
using timed automata as the input formalism, in which we assume that the
attacker has access (only) to the system execution time. First, we address the
following execution-time opacity problem: given a timed system modeled by a
timed automaton, given a secret location and a final location, synthesize the
execution times from the initial location to the final location for which one
cannot deduce whether the secret location was visited. This means that for any
such execution time, the system is opaque: either the final location is not
reachable, or it is reachable with that execution time for both a run visiting
and a run not visiting the secret location. We also address the full
execution-time opacity problem, asking whether the system is opaque for all
execution times; we also study a weak counterpart. Second, we add timing
parameters, which are a way to configure a system: we identify a subclass of
parametric timed automata with some decidability results. In addition, we
devise a semi-algorithm for synthesizing timing parameter valuations
guaranteeing that the resulting system is opaque. Third, we report on problems
when the secret has itself an expiration date, thus defining expiring
execution-time opacity problems. We finally show that our method can also apply
to program analysis with configurable internal timings.Comment: In Proceedings TiCSA 2023, arXiv:2310.18720. This invited paper
mainly summarizes results on opacity from two recent works published in ToSEM
(2022) and at ICECCS 2023, providing unified notations and concept names for
the sake of consistency. In addition, we prove a few original results absent
from these work
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