104 research outputs found
Separability in the Ambient Logic
The \it{Ambient Logic} (AL) has been proposed for expressing properties of
process mobility in the calculus of Mobile Ambients (MA), and as a basis for
query languages on semistructured data. We study some basic questions
concerning the discriminating power of AL, focusing on the equivalence on
processes induced by the logic . As underlying calculi besides MA we
consider a subcalculus in which an image-finiteness condition holds and that we
prove to be Turing complete. Synchronous variants of these calculi are studied
as well. In these calculi, we provide two operational characterisations of
: a coinductive one (as a form of bisimilarity) and an inductive one
(based on structual properties of processes). After showing to be stricly
finer than barbed congruence, we establish axiomatisations of on the
subcalculus of MA (both the asynchronous and the synchronous version), enabling
us to relate to structural congruence. We also present some
(un)decidability results that are related to the above separation properties
for AL: the undecidability of on MA and its decidability on the
subcalculus.Comment: logical methods in computer science, 44 page
Resource Bisimilarity in Petri Nets is Decidable
Petri nets are a popular formalism for modeling and analyzing distributed
systems. Tokens in Petri net models can represent the control flow state or
resources produced/consumed by transition firings. We define a resource as a
part (submultiset) of the Petri net marking and call two resources equivalent
iff replacing one of them with another in any marking does not change the
observable Petri net behavior. We investigate the resource similarity and the
resource bisimilarity -- congruent restrictions of the bisimulation equivalence
on Petri net markings and prove that the resource bisimilarity is decidable in
contrast to the resource similarity.Comment: New version for submission to the journa
Decidability Issues for Petri Nets
This is a survey of some decidability results for Petri nets, covering the last three decades. The presentation is structured around decidability of specific properties, various behavioural equivalences and finally the model checking problem for temporal logics
Beyond Language Equivalence on Visibly Pushdown Automata
We study (bi)simulation-like preorder/equivalence checking on the class of
visibly pushdown automata and its natural subclasses visibly BPA (Basic Process
Algebra) and visibly one-counter automata. We describe generic methods for
proving complexity upper and lower bounds for a number of studied preorders and
equivalences like simulation, completed simulation, ready simulation, 2-nested
simulation preorders/equivalences and bisimulation equivalence. Our main
results are that all the mentioned equivalences and preorders are
EXPTIME-complete on visibly pushdown automata, PSPACE-complete on visibly
one-counter automata and P-complete on visibly BPA. Our PSPACE lower bound for
visibly one-counter automata improves also the previously known DP-hardness
results for ordinary one-counter automata and one-counter nets. Finally, we
study regularity checking problems for visibly pushdown automata and show that
they can be decided in polynomial time.Comment: Final version of paper, accepted by LMC
The hitchhiker's guide to decidability and complexity of equivalence properties in security protocols
International audiencePrivacy-preserving security properties in cryptographic protocols are typically modelled by observational equivalences in process calculi such as the applied pi-calulus. We survey decidability and complexity results for the automated verification of such equivalences, casting existing results in a common framework which allows for a precise comparison. This unified view, beyond providing a clearer insight on the current state of the art, allowed us to identify some variations in the statements of the decision problems-sometimes resulting in different complexity results. Additionally, we prove a couple of novel or strengthened results
Behavioural Preorders on Stochastic Systems - Logical, Topological, and Computational Aspects
Computer systems can be found everywhere: in space, in our homes, in our
cars, in our pockets, and sometimes even in our own bodies. For concerns of
safety, economy, and convenience, it is important that such systems work
correctly. However, it is a notoriously difficult task to ensure that the
software running on computers behaves correctly.
One approach to ease this task is that of model checking, where a model of
the system is made using some mathematical formalism. Requirements expressed in
a formal language can then be verified against the model in order to give
guarantees that the model satisfies the requirements.
For many computer systems, time is an important factor. As such, we need our
formalisms and requirement languages to be able to incorporate real time.
We therefore develop formalisms and algorithms that allow us to compare and
express properties about real-time systems. We first introduce a logical
formalism for reasoning about upper and lower bounds on time, and study the
properties of this formalism, including axiomatisation and algorithms for
checking when a formula is satisfied.
We then consider the question of when a system is faster than another system.
We show that this is a difficult question which can not be answered in general,
but we identify special cases where this question can be answered. We also show
that under this notion of faster-than, a local increase in speed may lead to a
global decrease in speed, and we take step towards avoiding this.
Finally, we consider how to compare the real-time behaviour of systems not
just qualitatively, but also quantitatively. Thus, we are interested in knowing
how much one system is faster or slower than another system. This is done by
introducing a distance between systems. We show how to compute this distance
and that it behaves well with respect to certain properties.Comment: PhD dissertation from Aalborg Universit
Temporal Logic with Recursion
We introduce extensions of the standard temporal logics CTL and LTL with a recursion operator that takes propositional arguments. Unlike other proposals for modal fixpoint logics of high expressive power, we obtain logics that retain some of the appealing pragmatic advantages of CTL and LTL, yet have expressive power beyond that of the modal ?-calculus or MSO. We advocate these logics by showing how the recursion operator can be used to express interesting non-regular properties. We also study decidability and complexity issues of the standard decision problems
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