WRAPPING INTO DEVS SIMULATOR: A STUDY CASE
Gauthier Quesnel, Rapha®el Duboz and ¥ Eric Ramat
Laboratoire d'Informatique du Littoral
Universit¥e du littoral càot¥e d'opale
50, rue Ferdinand Buisson - BP 719
62228 CALAIS cedex FRANCE
quesnel@lil.univ-littoral.fr
Abstract
In this article, we study the wrapping technique to manage
existing models in a particular framework (the Virtual
Laboratory Environment ñ VLE). We deal with the
wrapping technique which consists in connecting existing
simulators models to DEVS compliant simulators.
Our approach is illustrated with a simple example: the
coupling of an ordinal differential equations system, a
DEVS model and a Petri net.
1 INTRODUCTION
Nowadays, it is recognised that multimodeling is a
powerful concept for the modeling and simulation of
large complex systems. At the end of 80's, P.A. Fishwick
and B.P. Zeigler (Fishwick and Zeigler, 1992)
introduced the multimodeling basis concepts. One
can dene multi-models as large models which are
composed of different types of models (i.e. different
paradigms) (Fishwick, 1995). Concepts like renement
and hierarchical composition are basis of multimodeling.
The rst describes the decomposition of one model
into several other ones in order to rene the behaviour
of the composed model. The last denes the opposite
process: it is say models aggregation. In this context, a
major issue is how to deal with the coupling of heterogeneous
models. Several works deal with the coupling
of heterogeneous models. For a review of concepts and
techniques, see the book of B.P. Zeigler et. al. (Zeigler
et al., 2000). With DEVS, Discrete Event System
Specication (Zeigler, 1976), B.P. Zeigler has provided
formal basis for the construction of coupled model in a
network or graph manner. If models we want to couple
are specied in a unique formalism, it does not appear
unsolvable problems, whereas the coupling of models
which are formally different can lead to several coupling
strategies.
The work presented here takes place in the eld of
formally heterogeneous models coupling. To tackle this
issue, we briey recall concepts like mapping and wrapping.
Then we give example of ìformalî wrapping and
show the feasibility with a particular and very simple
application.
1.1 Heterogeneous Models Coupling
In their book, B.P. Zeigler et. al. give the formal basis
for the specication of multi-formalism models. In
the same way, H. Vangheluwe proposes a framework for
multi-paradigm modeling and simulation (Vangheluwe
et al., 2002). In all those works, the DEVS formalism
appears as the common denominator for the integration
of heterogeneous models. DEVS provides two way for
the integration of non-DEVS models into DEVS simulator:
Mapping and Wrapping:
Mapping : Mapping concept means to nd a total
equivalence between a existing formalism and
DEVS. We can nd an example in Jacques and
Wainer's works for the mapping of Petri nets into
DEVS (Jacques and Wainer, 2002).
Wrapping : Wrapping means to build an algorithm
that is compatible with DEVS abstract simulators
i.e. to develop a functional interface between a particular
model and a DEVS simulator.
In this paper, we propose to deal with wrapping. As
we have applications in ecology (Duboz and Ramat,
2003), we need to address systems complexity. Wrapping
seems to be a powerful mean to achieve it. We have
developed a platform (Ramat and Preux, 2003). Initially,
VLE only deals with agent based modeling. This
platform is now oriented toward the integration of heterogeneous
models. Actually, VLE uses the DEVS formalism
and abstract simulators (Zeigler et al., 2000) for
coupling models by integrating the concept of DEVS-
.....