18 research outputs found
Results on Alternating-Time Temporal Logics with Linear Past
We investigate the succinctness gap between two known equally-expressive and different linear-past extensions of standard CTL^* (resp., ATL^*). We establish by formal non-trivial arguments that the "memoryful" linear-past extension (the history leading to the current state is taken into account) can be exponentially more succinct than the standard "local" linear-past extension (the history leading to the current state is forgotten). As a second contribution, we consider the ATL-like fragment, denoted ATL_{lp}, of the known "memoryful" linear-past extension of ATL^{*}. We show that ATL_{lp} is strictly more expressive than ATL, and interestingly, it can be exponentially more succinct than the more expressive logic ATL^{*}. Moreover, we prove that both satisfiability and model-checking for the logic ATL_{lp} are Exptime-complete
IST Austria Technical Report
There is recently a significant effort to add quantitative objectives to formal verification and synthesis. We introduce and investigate the extension of temporal logics with quantitative atomic assertions, aiming for a general and flexible framework for quantitative-oriented specifications. In the heart of quantitative objectives lies the accumulation of values along a computation. It is either the accumulated summation, as with the energy objectives, or the accumulated average, as with the mean-payoff objectives. We investigate the extension of temporal logics with the prefix-accumulation assertions Sum(v) ≥ c and Avg(v) ≥ c, where v is a numeric variable of the system, c is a constant rational number, and Sum(v) and Avg(v) denote the accumulated sum and average of the values of v from the beginning of the computation up to the current point of time. We also allow the path-accumulation assertions LimInfAvg(v) ≥ c and LimSupAvg(v) ≥ c, referring to the average value along an entire computation. We study the border of decidability for extensions of various temporal logics. In particular, we show that extending the fragment of CTL that has only the EX, EF, AX, and AG temporal modalities by prefix-accumulation assertions and extending LTL with path-accumulation assertions, result in temporal logics whose model-checking problem is decidable. The extended logics allow to significantly extend the currently known energy and mean-payoff objectives. Moreover, the prefix-accumulation assertions may be refined with “controlled-accumulation”, allowing, for example, to specify constraints on the average waiting time between a request and a grant. On the negative side, we show that the fragment we point to is, in a sense, the maximal logic whose extension with prefix-accumulation assertions permits a decidable model-checking procedure. Extending a temporal logic that has the EG or EU modalities, and in particular CTL and LTL, makes the problem undecidable
08171 Abstracts Collection -- Beyond the Finite: New Challenges in Verification and Semistructured Data
From 20.04. to 25.04.2008, the Dagstuhl Seminar 08171 ``Beyond the Finite: New Challenges in Verification and Semistructured Data\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Model Checking Flat Freeze LTL on One-Counter Automata
Freeze LTL is a temporal logic with registers that is suitable for specifying
properties of data words. In this paper we study the model checking problem for
Freeze LTL on one-counter automata. This problem is known to be undecidable in
general and PSPACE-complete for the special case of deterministic one-counter
automata. Several years ago, Demri and Sangnier investigated the model checking
problem for the flat fragment of Freeze LTL on several classes of counter
automata and posed the decidability of model checking flat Freeze LTL on
one-counter automata as an open problem. In this paper we resolve this problem
positively, utilising a known reduction to a reachability problem on
one-counter automata with parameterised equality and disequality tests. Our
main technical contribution is to show decidability of the latter problem by
translation to Presburger arithmetic
Automated Temporal Equilibrium Analysis: Verification and Synthesis of Multi-Player Games
In the context of multi-agent systems, the rational verification problem is
concerned with checking which temporal logic properties will hold in a system
when its constituent agents are assumed to behave rationally and strategically
in pursuit of individual objectives. Typically, those objectives are expressed
as temporal logic formulae which the relevant agent desires to see satisfied.
Unfortunately, rational verification is computationally complex, and requires
specialised techniques in order to obtain practically useable implementations.
In this paper, we present such a technique. This technique relies on a
reduction of the rational verification problem to the solution of a collection
of parity games. Our approach has been implemented in the Equilibrium
Verification Environment (EVE) system. The EVE system takes as input a model of
a concurrent/multi-agent system represented using the Simple Reactive Modules
Language (SRML), where agent goals are represented as Linear Temporal Logic
(LTL) formulae, together with a claim about the equilibrium behaviour of the
system, also expressed as an LTL formula. EVE can then check whether the LTL
claim holds on some (or every) computation of the system that could arise
through agents choosing Nash equilibrium strategies; it can also check whether
a system has a Nash equilibrium, and synthesise individual strategies for
players in the multi-player game. After presenting our basic framework, we
describe our new technique and prove its correctness. We then describe our
implementation in the EVE system, and present experimental results which show
that EVE performs favourably in comparison to other existing tools that support
rational verification