1,973 research outputs found
Structural and Behavioural Equivalences of Networks
We define an algebraic language for networks of synchronously communicating
processes. A node in the Network may have several ports; a port is either
external to the whole network or connected through a link to another
port. The language contains two types of operations: parallel composition
of two networks, and interlinking of two external ports within a network.
We interpret this language in two ways: first we give a structural
semantics, where terms are mapped to graphs representing the structure of
networks, and second we give a behavioural semantics, where terms are
mapped to behaviour schemes. A schema corresponds to a behaviour
parameterised on the behaviours of the network nodes. These semantics give
rise to structural and behavioural equivalences.
We compare the equivalences and give sound and complete axiomatisations
GSOS for non-deterministic processes with quantitative aspects
Recently, some general frameworks have been proposed as unifying theories for
processes combining non-determinism with quantitative aspects (such as
probabilistic or stochastically timed executions), aiming to provide general
results and tools. This paper provides two contributions in this respect.
First, we present a general GSOS specification format (and a corresponding
notion of bisimulation) for non-deterministic processes with quantitative
aspects. These specifications define labelled transition systems according to
the ULTraS model, an extension of the usual LTSs where the transition relation
associates any source state and transition label with state reachability weight
functions (like, e.g., probability distributions). This format, hence called
Weight Function SOS (WFSOS), covers many known systems and their bisimulations
(e.g. PEPA, TIPP, PCSP) and GSOS formats (e.g. GSOS, Weighted GSOS,
Segala-GSOS, among others).
The second contribution is a characterization of these systems as coalgebras
of a class of functors, parametric on the weight structure. This result allows
us to prove soundness of the WFSOS specification format, and that
bisimilarities induced by these specifications are always congruences.Comment: In Proceedings QAPL 2014, arXiv:1406.156
Modelling Probabilistic Wireless Networks
We propose a process calculus to model high level wireless systems, where the
topology of a network is described by a digraph. The calculus enjoys features
which are proper of wireless networks, namely broadcast communication and
probabilistic behaviour. We first focus on the problem of composing wireless
networks, then we present a compositional theory based on a probabilistic
generalisation of the well known may-testing and must-testing pre- orders.
Also, we define an extensional semantics for our calculus, which will be used
to define both simulation and deadlock simulation preorders for wireless
networks. We prove that our simulation preorder is sound with respect to the
may-testing preorder; similarly, the deadlock simulation pre- order is sound
with respect to the must-testing preorder, for a large class of networks. We
also provide a counterexample showing that completeness of the simulation
preorder, with respect to the may testing one, does not hold. We conclude the
paper with an application of our theory to probabilistic routing protocols
Characterizing Behavioural Congruences for Petri Nets
We exploit a notion of interface for Petri nets in order to design a set of net combinators. For such a calculus of nets, we focus on the behavioural congruences arising from four simple notions of behaviour, viz., traces, maximal traces, step, and maximal step traces, and from the corresponding four notions of bisimulation, viz., weak and weak step bisimulation and their maximal versions. We characterize such congruences via universal contexts and via games, providing in such a way an understanding of their discerning powers
Bisimulation of Labelled State-to-Function Transition Systems Coalgebraically
Labeled state-to-function transition systems, FuTS for short, are
characterized by transitions which relate states to functions of states over
general semirings, equipped with a rich set of higher-order operators. As such,
FuTS constitute a convenient modeling instrument to deal with process languages
and their quantitative extensions in particular. In this paper, the notion of
bisimulation induced by a FuTS is addressed from a coalgebraic point of view. A
correspondence result is established stating that FuTS-bisimilarity coincides
with behavioural equivalence of the associated functor. As generic examples,
the equivalences underlying substantial fragments of major examples of
quantitative process algebras are related to the bisimilarity of specific FuTS.
The examples range from a stochastic process language, PEPA, to a language for
Interactive Markov Chains, IML, a (discrete) timed process language, TPC, and a
language for Markov Automata, MAL. The equivalences underlying these languages
are related to the bisimilarity of their specific FuTS. By the correspondence
result coalgebraic justification of the equivalences of these calculi is
obtained. The specific selection of languages, besides covering a large variety
of process interaction models and modelling choices involving quantities,
allows us to show different classes of FuTS, namely so-called simple FuTS,
combined FuTS, nested FuTS, and general FuTS
Monitoring Networks through Multiparty Session Types
In large-scale distributed infrastructures, applications are realised through communications among distributed components. The need for methods for assuring safe interactions in such environments is recognized, however the existing frameworks, relying on centralised verification or restricted specification methods, have limited applicability. This paper proposes a new theory of monitored π-calculus with dynamic usage of multiparty session types (MPST), offering a rigorous foundation for safety assurance of distributed components which asynchronously communicate through multiparty sessions. Our theory establishes a framework for semantically precise decentralised run-time enforcement and provides reasoning principles over monitored distributed applications, which complement existing static analysis techniques. We introduce asynchrony through the means of explicit routers and global queues, and propose novel equivalences between networks, that capture the notion of interface equivalence, i.e. equating networks offering the same services to a user. We illustrate our static-dynamic analysis system with an ATM protocol as a running example and justify our theory with results: satisfaction equivalence, local/global safety and transparency, and session fidelity
Lean and Full Congruence Formats for Recursion
In this paper I distinguish two (pre)congruence requirements for semantic
equivalences and preorders on processes given as closed terms in a system
description language with a recursion construct. A lean congruence preserves
equivalence when replacing closed subexpressions of a process by equivalent
alternatives. A full congruence moreover allows replacement within a recursive
specification of subexpressions that may contain recursion variables bound
outside of these subexpressions.
I establish that bisimilarity is a lean (pre)congruence for recursion for all
languages with a structural operational semantics in the ntyft/ntyxt format.
Additionally, it is a full congruence for the tyft/tyxt format.Comment: To appear in: Proc. LICS'17, Reykjavik, Iceland, IEE
Deciding equivalence-based properties using constraint solving
Formal methods have proved their usefulness for analyzing the security of protocols. Most existing results focus on trace properties like secrecy or authentication. There are however several security properties, which cannot be defined (or cannot be naturally defined) as trace properties and require a notion of behavioural equivalence. Typical examples are anonymity, privacy related properties or statements closer to security properties used in cryptography.
In this paper, we consider three notions of equivalence defined in the applied pi calculus: observational equivalence, may-testing equivalence, and trace equivalence. First, we study the relationship between these three notions. We show that for determinate processes, observational equivalence actually coincides with trace equivalence, a notion simpler to reason with. We exhibit a large class of determinate processes, called simple processes, that capture most existing protocols and cryptographic primitives. While trace equivalence and may-testing equivalence seem very similar, we show that may-testing equivalence is actually strictly stronger than trace equivalence. We prove that the two notions coincide for image-finite processes, such as processes without replication.
Second, we reduce the decidability of trace equivalence (for finite processes) to deciding symbolic equivalence between sets of constraint systems. For simple processes without replication and with trivial else branches, it turns out that it is actually sufficient to decide symbolic equivalence between pairs of positive constraint systems. Thanks to this reduction and relying on a result first proved by M. Baudet, this yields the first decidability result of observational equivalence for a general class of equational theories (for processes without else branch nor replication). Moreover, based on another decidability result for deciding equivalence between sets of constraint systems, we get decidability of trace equivalence for processes with else branch for standard primitives
A Calculus of Mobility and Communication for Ubiquitous Computing
We propose a Calculus of Mobility and Communication (CMC) for the modelling
of mobility, communication and context-awareness in the setting of ubiquitous
computing. CMC is an ambient calculus with the in and out capabilities of
Cardelli and Gordon's Mobile Ambients. The calculus has a new form of global
communication similar to that in Milner's CCS. In CMC an ambient is tagged with
a set of ports that agents executing inside the ambient are allowed to
communicate on. It also has a new context-awareness feature that allows
ambients to query their location. We present reduction semantics and labelled
transition system semantics of CMC and prove that the semantics coincide. A new
notion of behavioural equivalence is given by defining capability barbed
bisimulation and congruence which is proved to coincide with barbed
bisimulation congruence. The expressiveness of the calculus is illustrated by
two case studies.Comment: In Proceedings WWV 2015, arXiv:1508.0338
Automated Netlist Generation for 3D Electrothermal and Electromagnetic Field Problems
We present a method for the automatic generation of netlists describing
general three-dimensional electrothermal and electromagnetic field problems.
Using a pair of structured orthogonal grids as spatial discretisation, a
one-to-one correspondence between grid objects and circuit elements is obtained
by employing the finite integration technique. The resulting circuit can then
be solved with any standard available circuit simulator, alleviating the need
for the implementation of a custom time integrator. Additionally, the approach
straightforwardly allows for field-circuit coupling simulations by
appropriately stamping the circuit description of lumped devices. As the
computational domain in wave propagation problems must be finite, stamps
representing absorbing boundary conditions are developed as well.
Representative numerical examples are used to validate the approach. The
results obtained by circuit simulation on the generated netlists are compared
with appropriate reference solutions.Comment: This is a pre-print of an article published in the Journal of
Computational Electronics. The final authenticated version is available
online at: https://dx.doi.org/10.1007/s10825-019-01368-6. All numerical
results can be reproduced by the Matlab code openly available at
https://github.com/tc88/ANTHE
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