365 research outputs found
Quantitative Games under Failures
We study a generalisation of sabotage games, a model of dynamic network games
introduced by van Benthem. The original definition of the game is inherently
finite and therefore does not allow one to model infinite processes. We propose
an extension of the sabotage games in which the first player (Runner) traverses
an arena with dynamic weights determined by the second player (Saboteur). In
our model of quantitative sabotage games, Saboteur is now given a budget that
he can distribute amongst the edges of the graph, whilst Runner attempts to
minimise the quantity of budget witnessed while completing his task. We show
that, on the one hand, for most of the classical cost functions considered in
the literature, the problem of determining if Runner has a strategy to ensure a
cost below some threshold is EXPTIME-complete. On the other hand, if the budget
of Saboteur is fixed a priori, then the problem is in PTIME for most cost
functions. Finally, we show that restricting the dynamics of the game also
leads to better complexity
Approaching the Coverability Problem Continuously
The coverability problem for Petri nets plays a central role in the
verification of concurrent shared-memory programs. However, its high
EXPSPACE-complete complexity poses a challenge when encountered in real-world
instances. In this paper, we develop a new approach to this problem which is
primarily based on applying forward coverability in continuous Petri nets as a
pruning criterion inside a backward coverability framework. A cornerstone of
our approach is the efficient encoding of a recently developed polynomial-time
algorithm for reachability in continuous Petri nets into SMT. We demonstrate
the effectiveness of our approach on standard benchmarks from the literature,
which shows that our approach decides significantly more instances than any
existing tool and is in addition often much faster, in particular on large
instances.Comment: 18 pages, 4 figure
Minimal Coverability Set for Petri Nets: Karp and Miller Algorithm with Pruning
This paper presents the Monotone-Pruning algorithm (MP) for computing the minimal coverability set of Petri nets. The original Karp and Miller algorithm (K&M) unfolds the reachability graph of a Petri net and uses acceleration on branches to ensure termination. The MP algorithm improves the K&M algorithm by adding pruning between branches of the K&M tree. This idea was first introduced in the Minimal Coverability Tree algorithm (MCT), however it was recently shown to be incomplete. The MP algorithm can be viewed as the MCT algorithm with a slightly more aggressive pruning strategy which ensures completeness. Experimental results show that this algorithm is a strong improvement over the K&M algorithm as it dramatically reduces the exploration tree
Incremental, Inductive Coverability
We give an incremental, inductive (IC3) procedure to check coverability of
well-structured transition systems. Our procedure generalizes the IC3 procedure
for safety verification that has been successfully applied in finite-state
hardware verification to infinite-state well-structured transition systems. We
show that our procedure is sound, complete, and terminating for downward-finite
well-structured transition systems---where each state has a finite number of
states below it---a class that contains extensions of Petri nets, broadcast
protocols, and lossy channel systems.
We have implemented our algorithm for checking coverability of Petri nets. We
describe how the algorithm can be efficiently implemented without the use of
SMT solvers. Our experiments on standard Petri net benchmarks show that IC3 is
competitive with state-of-the-art implementations for coverability based on
symbolic backward analysis or expand-enlarge-and-check algorithms both in time
taken and space usage.Comment: Non-reviewed version, original version submitted to CAV 2013; this is
a revised version, containing more experimental results and some correction
O tratamento da polissemia e da homonÃmia nos learner's dictionaries: subsÃdios da semântica cognitiva para a disposição das acepções
No âmbito lexicográfico, diversas são as questões impostas pela consideração dos fenômenos da polissemia e da homonÃmia. Neste trabalho, abordamos dois problemas centrais: (i) a solução adotada para a estruturação dos verbetes (solução polissêmica ou solução homonÃmica) e (ii) os critérios empregados para a organização das acepções dentro dos verbetes. Para isso, apresentamos análises de itens lexicais presentes nos quatro principais learner’s dictionaries – CALD (2008), COBUILD (2006), LDCE (2009) e OALD (2005)1. Nelas constatamos que não há homogeneidade nas soluções empregadas, tanto entre as obras quanto dentro da mesma obra para o tratamento do mesmo fenômeno, e que o critério empregado pelos dicionários para a organização das acepções, a frequência, é problemático, tanto por questões anteriores a sua aplicação quanto por problemas exclusivos a esse critério. Dessa forma, buscamos na concepção de polissemia da Semântica Cognitiva um modelo de descrição que auxiliasse na disposição das acepções nos verbetes de learner’s dictionaries. Ao final, apresentamos nossa sugestão de verbete para o item lexical band. ConcluÃmos com uma avaliação das questões que nosso modelo consegue tratar de forma mais efetiva e trazemos ainda problemas para os quais continuamos sem solução
A Graph-Based Semantics Workbench for Concurrent Asynchronous Programs
A number of novel programming languages and libraries have been proposed that
offer simpler-to-use models of concurrency than threads. It is challenging,
however, to devise execution models that successfully realise their
abstractions without forfeiting performance or introducing unintended
behaviours. This is exemplified by SCOOP---a concurrent object-oriented
message-passing language---which has seen multiple semantics proposed and
implemented over its evolution. We propose a "semantics workbench" with fully
and semi-automatic tools for SCOOP, that can be used to analyse and compare
programs with respect to different execution models. We demonstrate its use in
checking the consistency of semantics by applying it to a set of representative
programs, and highlighting a deadlock-related discrepancy between the principal
execution models of the language. Our workbench is based on a modular and
parameterisable graph transformation semantics implemented in the GROOVE tool.
We discuss how graph transformations are leveraged to atomically model
intricate language abstractions, and how the visual yet algebraic nature of the
model can be used to ascertain soundness.Comment: Accepted for publication in the proceedings of FASE 2016 (to appear
Context-Bounded Analysis For Concurrent Programs With Dynamic Creation of Threads
Context-bounded analysis has been shown to be both efficient and effective at
finding bugs in concurrent programs. According to its original definition,
context-bounded analysis explores all behaviors of a concurrent program up to
some fixed number of context switches between threads. This definition is
inadequate for programs that create threads dynamically because bounding the
number of context switches in a computation also bounds the number of threads
involved in the computation. In this paper, we propose a more general
definition of context-bounded analysis useful for programs with dynamic thread
creation. The idea is to bound the number of context switches for each thread
instead of bounding the number of switches of all threads. We consider several
variants based on this new definition, and we establish decidability and
complexity results for the analysis induced by them
Preventie van valincidenten bij thuiswonende ouderen: een kostenbesparende interventie?
Nationale en internationale cijfers tonen aan dat 1 op 3 thuiswonende 65-plussers en nagenoeg de helft van de 80-plussers
minstens eenmaal per jaar valt. Bij ongeveer 40% van hen resulteert dit in een letsel. Ongeveer 10% van de valpartijen
bij ouderen leidt tot ernstige letsels, waaronder heupfracturen (1-2%), andere fracturen (3-5%) en letsels van de weke delen
en hoofdtrauma (5%)
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