4,831 research outputs found
The Spectrum of Strong Behavioral Equivalences for Nondeterministic and Probabilistic Processes
We present a spectrum of trace-based, testing, and bisimulation equivalences
for nondeterministic and probabilistic processes whose activities are all
observable. For every equivalence under study, we examine the discriminating
power of three variants stemming from three approaches that differ for the way
probabilities of events are compared when nondeterministic choices are resolved
via deterministic schedulers. We show that the first approach - which compares
two resolutions relatively to the probability distributions of all considered
events - results in a fragment of the spectrum compatible with the spectrum of
behavioral equivalences for fully probabilistic processes. In contrast, the
second approach - which compares the probabilities of the events of a
resolution with the probabilities of the same events in possibly different
resolutions - gives rise to another fragment composed of coarser equivalences
that exhibits several analogies with the spectrum of behavioral equivalences
for fully nondeterministic processes. Finally, the third approach - which only
compares the extremal probabilities of each event stemming from the different
resolutions - yields even coarser equivalences that, however, give rise to a
hierarchy similar to that stemming from the second approach.Comment: In Proceedings QAPL 2013, arXiv:1306.241
Conformance Verification of Normative Specifications using C-O Diagrams
C-O Diagrams have been introduced as a means to have a visual representation
of normative texts and electronic contracts, where it is possible to represent
the obligations, permissions and prohibitions of the different signatories, as
well as what are the penalties in case of not fulfillment of their obligations
and prohibitions. In such diagrams we are also able to represent absolute and
relative timing constrains.
In this paper we consider a formal semantics for C-O Diagrams based on a
network of timed automata and we present several relations to check the
consistency of a contract in terms of realizability, to analyze whether an
implementation satisfies the requirements defined on its contract, and to
compare several implementations using the executed permissions as criteria.Comment: In Proceedings FLACOS 2012, arXiv:1209.169
Distributed System Contract Monitoring
The use of behavioural contracts, to specify, regulate and verify systems, is
particularly relevant to runtime monitoring of distributed systems. System
distribution poses major challenges to contract monitoring, from
monitoring-induced information leaks to computation load balancing,
communication overheads and fault-tolerance. We present mDPi, a location-aware
process calculus, for reasoning about monitoring of distributed systems. We
define a family of Labelled Transition Systems for this calculus, which allow
formal reasoning about different monitoring strategies at different levels of
abstractions. We also illustrate the expressivity of the calculus by showing
how contracts in a simple contract language can be synthesised into different
mDPi monitors.Comment: In Proceedings FLACOS 2011, arXiv:1109.239
Test Derivation from Timed Automata
A real-time system is a discrete system whose state changes occur in real-numbered time [AH97]. For testing real-time systems, specification languages must be extended with constructs for expressing real-time constraints, the implementation relation must be generalized to consider the temporal dimension, and the data structures and algorithms used to generate tests must be revised to operate on a potentially infinite set of states
TAPAs: A Tool for the Analysis of Process Algebras
Process algebras are formalisms for modelling concurrent systems that permit mathematical reasoning with respect to a set of desired properties. TAPAs is a tool that can be used to support the use of process algebras to specify and analyze concurrent systems. It does not aim at guaranteeing high performances, but has been developed as a support to teaching. Systems are described as process algebras terms that are then mapped to labelled transition systems (LTSs). Properties are verified either by checking equivalence of concrete and abstract systems descriptions, or by model checking temporal formulae over the obtained LTS. A key feature of TAPAs, that makes it particularly suitable for teaching, is that it maintains a consistent double representation of each system both as a term and as a graph. Another useful didactical feature is the exhibition of counterexamples in case equivalences are not verified or the proposed formulae are not satisfied
When Are Two Workflows the Same?
In the area of workflow management, one is confronted with a large number of competing languages and the relations between them (e.g. relative expressiveness) are usually not clear. Moreover, even within the same language it is generally possible to express the same workflow in different ways, a feature known as variability. This paper aims at providing some of the formal groundwork for studying relative expressiveness and variability by defining notions of equivalence capturing different views on how workflow systems operate. Firstly, a notion of observational equivalence in the absence of silent steps is defined and related to classical bisimulation. Secondly, a number of equivalence notions in the presence of silent steps are defined. A distinction is made between the case where silent steps are visible (but not controllable) by the environment and the case where silent steps are not visible, i.e., there is an alternation between system events and environment interactions. It is shown that these notions of equivalence are different and do not coincide with classical notions of bisimulation with silent steps (e.g. weak and branching)
Quantitative testing semantics for non-interleaving
This paper presents a non-interleaving denotational semantics for the
?-calculus. The basic idea is to define a notion of test where the outcome is
not only whether a given process passes a given test, but also in how many
different ways it can pass it. More abstractly, the set of possible outcomes
for tests forms a semiring, and the set of process interpretations appears as a
module over this semiring, in which basic syntactic constructs are affine
operators. This notion of test leads to a trace semantics in which traces are
partial orders, in the style of Mazurkiewicz traces, extended with readiness
information. Our construction has standard may- and must-testing as special
cases
Comparing Refinements for Failure and Bisimulation Semantics
Refinement in bisimulation semantics is defined differently from refinement in failure semantics: in bisimulation semantics refinement is based on simulations between labelled transition systems, whereas in failure semantics refinement is based on inclusions between decorated traces systems. There exist however pairs of refinements, for bisimulation and failure semantics respectively, that have almost the same properties. Furthermore, each refinement in bisimulation semantics implies its counterpart in failure semantics, and conversely each refinement in failure semantics implies its counterpart in bisimulation semantics defined on the canonical form of the compared processes
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