Foundation publications

Here, thesis or proof of concepts that founded the main concepts of MECSYCO :

This work deals with complex system Modeling and Simulation (M&S). The particularity of such systems is the numerous heterogeneous entities in interaction involved inside them. This particularity leads to several organization layers and scientific domains. As a consequence, their study requests many perspectives (different temporal and spatial scales, different domains and formalisms, different granularities...). The challenge is the rigorous integration of these various system perspectives inside an M&S process. In other words, the difficulty is to define successive steps to follow in order to integrate several points of view inside the same model. Multi-modeling and co-simulation are promising approaches to do so. The underlying problem is to define a modular and hierarchical process fitted with a rigorous way to integrate heterogeneous components and which is supported by a software environment that covers the whole M&S cycle. MECSYCO (Multi-agent Environment for Complex SYstem CO-simulation) is a co-simulation middleware focusing on the reuse of existing models from other software. It relies on a software and formal DEVS-based wrapping, provides heterogeneity handling mechanisms and ensures a decentralized and modular co-simulation. MECSYCO deals with the heterogeneous component integration need but its M&S process does not have all the properties above-mentioned. Notably, the hierarchical modeling ability is missing. To overcome this, we propose to fit MECSYCO with a descriptive multi-modeling and co-simulation process that allows the hierarchical design of multi-models using models from other software. Our process is split into three steps: the atomic model integration, the composition (hierarchical multi-model construction) and finally the experimentation. We adopt a descriptive approach where a description file is linked to each product of these steps, these documents enable to manipulate them. The use of description files completes the integration steps, allows a hierarchical and modular multi-model design and isolates the experiments. Then we set up a development environment based on Domain Specific Languages (DSL) to support the description work, and we automate the transition from an experiment description to its effective co-simulation. This is a Model-Driven Engineering approach which allows us to put into practice our contribution by facilitating the modelers' work and by avoiding implementation mistakes. Our contribution fits MECSYCO with the hierarchical design property and with a DSL-based M&S environment while keeping its rigorous integration process and its modularity. Our work is evaluated on two examples. The first one renews a hybrid highway multi-model already implemented in MECSYCO, it shows the conservation of the middleware former properties. The second one is a simple thermal smart-building multi-model which highlights the incremental design of a multi-model and the integration of new components while putting our entire approach into practice.

Thesis

Modeling and simulation (M&S) of cyber-physical systems (CPS) can require representing components from three expertise fields: physics, information systems, and communication networks (IP). There is no universal simulator with all of the required skills, but we can gather and interconnect models provided by the communities, with a multi-model. The challenges are 1) integrating all heterogeneities in a multi-model (formalisms, representations, implementations), 2) integrating IP models in a way enabling them to represent the transport of application data produced by external models, and 3) integrating IP models in a way enabling them to complete each other, to be able to represent CPS heterogeneous IP networks. In order to meet these challenges, we relied our solution on the works around MECSYCO, a co-simulation platform based on the DEVS wrapping principle. We propose to define a comprehensive framework enabling to achieve DEVS wrapping of IP models, with 1) a structuration of different issue levels when integrating IP models in a co-simulation (goals and constraints of the wrapping) and 2) a proposition of a DEVS wrapping strategy for IP models and their simulators. We propose some evaluations of our approach, through the integration of two popular IP simulators, and concrete examples of CPS M&S (inter alia, with an example of a models interconnection between NS-3 and OMNeT++/INET, and an industrial application used by EDF R&D).

Thesis

This thesis is focused on the study of complex systems through a modeling and simulation (M&S) process. Most questions about such systems requiere to take simultaneously account of several points of view. Phenomena evolving at different (temporal and spatial) scales and at different levels of resolution (from micro to macro) have to be considered. Moreover, several expert skills belonging to different scientific fields are needed. The challenges are then to reconcile these heterogeneous points of view, and to integrate each domain tools (formalisms and simulation software) within the rigorous framework of the M&S process. In order to solve these issues, we mobilise notions from multi-level modeling, hybrid modeling, parallel simulation and software engineering. Regarding these fields, we study the complementarity of the AA4MM approach and the DEVS formalism into the scope of the model-driven engineering (MDE) approach. Our contribution is twofold. We propose the operational specifications of the MECSYCO co-simulation middleware enabling the parallel simulation of complex systems models in a rigorous and decentralized way. We also define an MDE approach enabling the non-ambiguous description of complex systems models and their automatic implementation in MECSYCO. We show the properties of our approach with several proofs of concept.

Thesis

This work has been done between the fields of ubiquitous networks and multi-agent based simulation. The main context is to study mutual influences existing between ubiquitous network performances and their users' behaviors. We have highlighted the need for reusing and coupling modelling and simulation softwares together in order to simultaneously integrate several abstraction levels in the study. We target those needs by a multi-agent approach and we propose a metamodel: AA4MM. The core idea in AA4MM is to build a society of models, simulators and simulation softwares that solves the core challenges of multi-modelling and simulation coupling in an homogeneous perspective. AA4MM major contributions are the possibility to easily reuse, to make interoperable and modular existing heterogeneous models and softwares, to manage scale changes and a simulation algorithm fully decentralized. We apply this metamodel to the field of ubiquitous networks in order to target the question of mutual influences between networks performances and users' behaviors.

Thesis

Most modeling and simulation (M&S) questions about cyber-physical systems (CPS) require expert skills belonging to different scientific fields. The challenges are then to integrate each domain's tools (formalism and simulation software) within the rigorous framework of M&S process. To answer this issue, we give the specifications of the MECSYCO co-simulation middle-ware which enables to interconnect several pre-existing and heterogeneous M&S tools, so they can simulate a whole CPS together. The middleware performs the co-simulation in a parallel, decentralized and distributable fashion thanks to its modular multi-agent architecture. In order to rigorously integrate tools which use different formalisms, the co-simulation engine of MECSYCO is based on DEVS. The central idea of MECSYCO is to use a DEVS wrapping strategy to integrate each tool into the middleware. Thus, heterogeneous tools can be homogeneously co-simulated in the form of a DEVS system. By using DEVS, MECSYCO benefits from the numerous scientific works which have demonstrated the integrative power of this formalism and gives crucial guidelines to rigorously design wrappers. We demonstrate that our discrete framework can integrate a vast amount of continuous M&S tools by wrapping the FMI standard. To this end, we take advantage of DEVS efforts of the literature (namely, the DEV&DESS hybrid formalism and QSS solvers) to design DEVS wrappers for FMU components. As a side-effect, this wrapping is not restricted to MECSYCO but can be applied in any DEVS-based platform. We evaluate MECSYCO with the proof of concept of a smart-heating use-case, where we co-simulate non DEVS-centric M&S tools.

Journal

Cyber-physical system representation is one of the current challenges in Modeling and Simulation. In fact, multi-domain modeling requires new approaches to rigorously deal with it. Co-simulation, one of the approaches, lets modelers use several M&S tools in collaboration. The challenge is to find a way to enable co-simulation use for non-IT experts while being aware of assumptions and limitations involved. This paper deals with co-simulation basic principles teaching through practice. we propose an iterative and modular co-simulation process supported by a DSL-based environment for the MECSYCO co-simulation platform. Through a thermal use case, we are able to introduce co-simulation in a 4 hours tutorial destined to our students. Efficient energy management is one of this century challenges. The current trend to deal with it is to build cyber-physical system (CPS) [Kleissl and Agarwal, 2010]. CPS are physical systems monitored and supervised by one or several computers through a communication networks [Ra-jkumar et al., 2010]. Smart-grids are examples of CPS where the energy network is coupled with a communication network to enable remote monitoring and control. The Modeling and Simulation (M&S) of such systems is one of the current challenges in M&S due to the inter-disciplinary issues they raise. It requests the development of new methods which deal with multi-domain by integrating each expert point of view in the same rigorous and efficient M&S activity. Co-simulation [Gomes et al., 2018] is a way to achieve it.

Jul Conference paper

Co-simulation is a key tool in the design and operation of a growing number of complex cyber-systems. But efficiently yet accurately combining continuous time components (such as FMUs) with event-based ones can be challenging, both from a modeling perspective and an operational, tools-oriented one. We propose a platform to tackle this problem building up on MECSYCO, a MAS-based DEVS wrapping platform dedicated to co-simulation. Relying on the ability of DEVS to integrate the DEV&DESS formalism -which offers a sound framework for describing hybrid models- we propose a DEV&DESS wrapper for FMU. This wrapper encapsulates a version of the DEV&DESS simulation algorithm for FMU components which is notably composed of: (1) a forecast strategy which searches for the next state-event; (2) a bisectional algorithm to approach the location of the state-change in an FMU. Our solution is implemented using Java and JavaFMI to control the FMU. Our sample case is the co-simulation of a barrel-filler factory implemented in different FMUs and event-based models. Compared to related works, our proposal is functional, generic, yet evolutionary, and benefits from the strong foundations of DEV&DESS.

Conference paper

Cyber-Physical Systems (smart grids, cities, homes, etc) are composed of computing resources, actuators and sensors , connected through IP networks. These IP networks involve many technologies. In order to help designing and evaluating these systems, we are studying the modeling and simulation of IP networks in this context. Since there is no universal IP simulator proposing a model library corresponding to all the required technologies, we propose a solution to make different major IP simulators, generally not interoperable, interact with one another in a same co-simulation. Moreover, they should also interact with simu-lators corresponding to other fields of expertise involved in the simulation, mostly related to the physical or social aspects of these systems (e.g. power models, traffic models, weather models, etc). In this paper, we propose to address these issues as a multi-modeling problem, by integrating well-known IP network simulators into a DEVS-based co-simulation platform. We propose some concepts, helping to split a network topology into several models, to create input/output ports inside them, and to integrate them to a DEVS multi-model. We illustrate our solution thanks to a use case, including interconnected event-based models executed both by NS-3 and OMNeT++, equation-based models and the co-simulation platform MECSYCO.

Conference paper

Mobile and Ubiquitous Computing is about interconnected computing resources embedded in our daily lives and providing contextual services to users. The real influence between user behavior and ubiquitous communication protocols performance and operation needs to be taken into account at the protocol design stage. Therefore, we provide a generic multi-modeling approach that allows us to couple a user behavior model with a network model. To allow both assessment and benchmarking of ubiquitous solutions, we define formal reference scenarios based on the selection of a set of environmental conditions (contexts). We illustrate the use of the framework through its application to the study of mutual influences of mobility models and ad hoc network protocols

Conference paper

Complex systems simulations generally involve the interaction of different scientific fields. Human economies, ecosystems or dynamic computer networks such as P2P are good examples. Since models and simulators already exist in those fields, designing the simulation as a society of interacting and co-evolving models appears attractive. Beyond the technical issues to make different simulators cooperate, the challenges are to make the co-evolution design and implementation easier for the users that rarely know intricate modelling and simulation tools, and to facilitate the collaboration of different experts. Agents and artefacts (A&A) paradigm simplifies the design and the implementation of a society of interacting and co-evolving models. That is, the addition, the removal or the interchange of models require less effort. Contrary to classical approaches, we have built a decentralized co-evolution architecture based upon A&A and a data-driven coordination model. In this article, beyond the architecture presentation, we focus on the benefit provided by A&A used for multiple models co-evolution.

Conference paper