Abstracts of talks at the Braga IFIP WG1.3 meeting
Abstracts of talks at the Braga IFIP WG1.3 meeting (March 23-24,
2007)
=== Friday, March 23rd, 2007
- 1 - Narciso MARTI-OLIET
Algebraic simulations
(slides)
(joint work with Jose Meseguer and Miguel Palomino)
In the first part of the talk we describe generalizations of
simulations in three
directions. First, by avoiding negation we relax
the condition on preservation
of atomic properties from equality to
containment; second, we consider
stuttering simulations, which are
useful to relate concurrent systems with
different levels of
atomicity; third, we allow different alphabets AP and AP' of
atomic
propositions so that an atomic proposition in AP is mapped to a
state
formula over AP'. A categorical viewpoint is the most natural
to understand
and organize these generalized simulations.
In the second part of the talk we prove several representability
results
showing that any Kripke structure can be represented by a
rewrite theory,
and that any generalized simulation can be represented
by a rewrite relation.
We consider four increasingly more general ways
of defining simulations
in rewriting logic: equational abstractions,
theory interpretations, simulation
maps as equationally defined
functions, and simulations given by rewrite
relations. The first two
techniques have been studied in detail in previous
papers. The third
one is illustrated here by means of an example showing
that a stack
machine correctly implements the operational semantics for a
simple
functional language. The fourth one is also illustrated by means of
a
communication protocol example proving in-order delivery of messages
in
the presence of an unreliable medium.
References:
J. Meseguer, M. Palomino, and N. Marti-Oliet.
Equational abstractions (extended version)
J. Meseguer, M. Palomino, and N. Marti-Oliet.
Algebraic Simulations
Both are available from
http://maude.sip.ucm.es/~miguelpt
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- 2 - Laure PETRUCCI
Modular construction of symbolic observation graph
(joint work with Kais Klai)
Model checking for Linear Time Logic (LTL) is usually based
on
converting the property into a Buchi automaton (or
tableau),
composing the automaton and the model, and finally checking
for
emptiness of the language of the composed system. The last step
is
the crucial stage of the verification process because of the
state
explosion problem, i.e. the exponential increase of the
number
of states w.r.t. the number of system components.
In this
work,
we present a symbolic and modular solution which builds, in a
modular
way, an observation graph represented in a non-symbolic way
but where the
nodes are essentially symbolic sets of states and the
edges either labelled by
events occurring in the formula or by
synchronisation actions between the
system components. Due to the
small number of events to be observed in a
typical formula, this graph
has a very moderate size and thus the complexity
time of verification
is negligible w.r.t. the time to build the observation
graph.
The preliminary evaluations we have achieved on standard examples
show
that our method outperforms both a non modular generation of the
symbolic
graph and the pure symbolic methods.
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- 4 - Marie-Claude GAUDEL
Uniform random sampling of traces in very large models
(joint work with Alain Denise, Sandrine-Dominique Gouraud,
Richard Lassaigne, Sylvain Peyronnet)
This talk presents some first results on how to perform uniform
random
walks (where every trace has the same probability to occur) in
very
large models. The models considered here are described in a
succinct
way as a set of communicating reactive modules. The method
relies
upon techniques for counting and drawing uniformly at random
words in
regular languages. Each module is considered as an automaton
defining
such a language. It is shown how it is possible to combine
local
uniform drawings of traces, and to obtain some global uniform
random
sampling, without construction of the global model.
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- 5 - Stefania GNESI
web page
A model checking approach for designing asynchronous extension of SOAP
(joint work with Maurice ter Beek, and Franco Mazzanti)
In this talk an action-state based logical framework for the analysis
and
verification of complex systems that relies on the definition of
doubly
labeled transition systems. The defined logic combines the
action
paradigm, classically used for describing systems using
labeled
transitions systems together with the predicates that are true
over
states as captured using Kripke structures as semantic model.
An
efficient model checker for this logic has been realized exploiting
an
on the fly algorithm. In the end of the talk the use of the logic
and
its model checker in the design phase of an asynchronous extension
of
SOAP is shown.
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- 7 - Luis Soares BARBOSA
slides
and web page
Revisiting invariants
(joint work with José N. Oliveira and Alexandra Silva )
We discuss the usefulness of reasoning about invariants for
software
components
coalgebraically in the allegory of binary
relations.
The novelty of our approach consists in establishing a
synergy between
a relational construct, Reynolds' Çrelation on
functionsÈ involved in
his abstraction theorem (traditionally employed
in explaining and reasoning
about parametric polymorphism),
and the
coalgebraic approach to bisimulations and invariants.
This synergy arises from the fact that, once
pointfree-transformed,
formulae in one domain Çlook likeÈ others in
the other domain.
We stress on this syntactic aspect of formal
reasoning,
a kind of "let-the-symbols-do-the-work" style of
calculation, often neglected
by too much emphasis on domain-specific,
semantic concerns.
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- 9 - Alexander KURZ
A characterisation of modal logics of rank 1
(joint work with J. Rosicky)
We show that a functor on a variety has a finitary presentation by
operations
and equations if and only if this functor preserves sifted
colimits. Moreover,
from the proof it follows that this presentation
is by equations of rank 1 (an
equation is of rank 1 if each variable
is in the scope of precisely one modal
operator). We also remark that
on the variety of Boolean algebras sifted
colimit preserving functors
and filtered colimit preserving functors (almost)
coincide.
This is joint work with J. Rosicky and one of the results of our paper
on
Strongly complete logics for coalgebras, available from my
home
page.
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== Saturday, March 24rd, 2007
- 13 - Till MOSSAKOWSKI
Heterogeneous proof scripts
The heterogeneous tool set integrates various languages, logics
and
proof tools. So far, proof management has been session based,
using
a graphical user interface. A proof script language (like the
ones
used by current interactive theorem provers) has the
advantage
that proof developments are made explicit and can be re-used
for
later developments. We introduce such as proof script language
for
Hets. It combines proof commands for the structured level
(using
the development graph calculus) with local theorem provers
for
specific logics. Proof scripts for the latter can be embedded
into
the scripts for Hets, such that we arrive at heterogeneous
proof
scripts.
Hets is available under:
here
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