Strategic Port Graph Rewriting: An Interactive Modelling and Analysis Framework

We present strategic portgraph rewriting as a basis for the implementation of visual modelling and analysis tools. The goal is to facilitate the specification, analysis and simulation of complex systems, using port graphs. A system is represented by an initial graph and a collection of graph rewriting rules, together with a user-defined strategy to control the application of rules. The strategy language includes constructs to deal with graph traversal and management of rewriting positions in the graph. We give a small-step operational semantics for the language, and describe its implementation in the graph transformation and visualisation tool PORGY.Comment: In Proceedings GRAPHITE 2014, arXiv:1407.767

On the Influence of the instance structure for metaheuristic performances -- Application to a graph drawing problem

International audienceMetaheuristics are now so common that for some classical hard combinatorial problems, there exist more than ten variants. Thus, the issue of comparing optimization methods is crucial. In this paper, we focus on one aspect of this question: the impact of the choice of the test instances on the metaheuristic performances and the possible link with the fitness landscape structure. We base our experimental framework on the arc crossing minimization problem for layered digraphs. We compare a hybridized genetic algorithm and a multistart descent which are among the best approaches to this problem. We worked on two instance families with various sizes and structural complexities: small graphs which are easy to draw on a standard size support, and large graphs specifically built for our experiments. We show that, for the smallest instances, there is no significant difference between methods whereas for graphs similar to those classically used nowadays in applications the genetic algorithm is better, and for the largest graphs (with a scaling factor up to $10^{300}$), the multistart descent is the best method. These results suggest that for ``structured'' fitness landscapes associated with real-life instances the GA exploits its implicit learning. On the other hand for very large landscapes with probably numerous local optima, only one exploration on a larger scale can be provided by local searches from a random starting point, cheap in computing effort

Un guide sur la toile pour sélectionner un logiciel de tracé de graphes

Nouvelle adresse du site : http://gvsr.polytech.univ-nantes.frNational audienceLes graphes permettent d'une part, en tant qu'objets combinatoires, de modéliser et d'analyser des systèmes de relations complexes entre des entités et d'autre part, de représenter ces relations sur des supports visuels afin de les rendre accessibles à un utilisateur non spécialiste. Si ces derniers sont rapidement devenus des outils privilégiés pour de nombreuses problématiques applicatives comme la découverte de relations non explicites en veille technologique, le choix d'une méthode de visualisation efficace reste encore très souvent une question ouverte pour l'utilisateur. Afin de guider ce dernier dans sa sélection, nous dressons une typologie succincte des principaux modes de représentation à savoir le tracé statique, le tracé interactif et le tracé des très grands graphes, et nous finissons par la présentation d'un nouveau site Web, dédié au référencement des logiciels de tracés de graphes. Le site est consultable à l'adresse : http://hulk.knowesis.fr/GVSR http://gvsr.polytech.univ-nantes.fr. Son originalité réside en particulier dans une présentation homogène des informations pertinentes mises en œuvre au travers d'un ensemble de fiches codées en XML

PORGY: a Visual Analytics Platform for System Modelling and Analysis Based on Graph Rewriting

PORGY is a visual environment for rule-based modelling based on port graphs and port graph rewrite rules whose application is steered by rewriting strategies. The focus of this demonstration is the visual and interactive features offered by PORGY, which facilitate an exploratory approach to model, simu- late and analyse different ways of applying the rules while recording the model evolution, as well as tracking and plotting system parameters

Découverte interactive de règles d'association via une interface visuelle

En nous appuyant sur des hypothèses majoritairement empruntées à des travaux sur les systèmes anthropocentrés d'aide à la décision, nous décrivons dans cet article un environnement interactif de fouille de règles d'association dans lequel l'utilisateur pilote le processus, en jouant le rôle d'une heuristique dans un environnement de recherche complexe. Afin de permettre à la fois une représentation visuelle accessible et une instanciation aisée des outils d'interactivité le modèle choisi est ici un graphe en niveaux - les niveaux étant associés aux cardinaux des sous-ensembles d'attributs des prémisses. Le processus a été déployé dans un logiciel prototype dont l'analyse des résultats ouvre de nouvelles perspectives sur l'analyse comportementale d'un utilisateur en situation de fouille

PORGY : réécriture et visualisation de graphes dynamiques

International audienceCet article présente les premiers résultats sur la visualisation et la manipulation interactive d'un système de réécriture de graphes. Nous sommes amenés à nous pencher sur la visualisation de graphes dont la topologie évolue au cours du temps selon des modifications dictées par des règles de réécriture. Le système doit non seulement de montrer le graphe qui évolue au cours du temps, mais il apparaît ici comme un atelier complet permettant d'étudier le système de réécriture lui-même. Il s'agit d'amener la visualisation en appui à l'étude du système de réécriture pour permettre de comprendre son comportement et d'identifier ses propriétés comme par exemple la convergence des calculs ou les configurations bloquantes. Outre les questions relatives au dessin des graphes qui font encore l'objet de travaux, le système se penche sur les problèmes d'identification de motifs et d'historique des réécritures. Nous abordons aussi les questions plus techniques relatives à la structure interne du système

PORGY: Interactive and Visual Reasoning with Graph Rewriting Systems

International audienceGraph rewriting systems have long been around in theoretical computer science, and are used as a computing model in discrete mathematics, algebra, mathematical logic or even linguistics. Graph rewriting systems operate on graphs by substituting local patterns. Starting from an initial graph, the system iterates transformation rules in a non necessarily deterministic way. The combination of rule applications turn the study of such a system into an involved task requiring high level expertise. The inherent complexity of graph rewriting systems motivated the use of graphical diagrams, even by experts, to convey ideas and theoretical concepts. In these situations, users are not experts in theoretical computer science but rather focus on how a graph rewriting system behaves as a model of the problem they study. Questions emerging from the target application nevertheless translate into questions about the rewriting system. The goal of this work is to allow users to experiment with a graph rewriting system, and reason about the system or the model it supports based on graphical representations of all its components. Visually reasoning about the system, domain experts are able to abstract and refine models, use simulation and deduction to compute or check postulated properties and make testable predictions about possible outcomes. PORGY possesses genuine features and appears to be the first system to offer multiple coordinated views, allowing users to visualize and manipulate the system at both a global and local scale

Labelled Port Graph – A Formal Structure for Models and Computations

International audienceWe present a general definition of labelled port graph that serves as a basis for the design of graph-based programming and modelling frameworks (syntax and semantics). We show that this structure provides the syntax for programs, which are composed of an initial graph, a set of rules and a strategy. Rules, represented as labelled port graphs, apply to states, also represented as labelled port graphs, and compute their successors according to the given strategy. The description of states, rules, and computations controlled by strategies, using labelled port graphs, is detailed and illustrated with examples from Porgy, a strategic port graph rewriting environment for the design of executable specifications of complex systems

Strategic Port Graph Rewriting: an Interactive Modelling Framework

International audienceWe present strategic port graph rewriting as a basis for the implementation of visual modelling tools. The goal is to facilitate the specification and programming tasks associated with the modelling of complex systems. A system is represented by an initial graph and a collection of graph rewrite rules, together with a user-defined strategy to control the application of rules. The traditional operators found in strategy languages for term rewriting have been adapted to deal with the more general setting of graph rewriting, and some new constructs have been included in the strategy language to deal with graph traversal and management of rewriting positions in the graph. We give a formal semantics for the language, and describe its implementation: the graph transformation and visualisation tool Porgy

Porgy : une plate-forme visuelle et interactive pour la réécriture de graphes : présentation lors de la journée Visu 2012

Voir http://visu2012.imag.fr/ pour plus d'informationsGraph rewriting systems (GRSs) operate on graphs by substituting local patterns according to a set of rewriting rules. The apparent simplicity of GRSs hides an incredible complexity and turns the study of these systems into an involved task requiring high-level expertise. We designed PORGY, an interactive visual environment to fully support GRSs related tasks, exploiting a long historical tradition of GRSs with node-link representations of graphs. PORGY enables rule-based modeling and simulation steering through graphical representations and direct manipulation of all GRSs components. This talk presents PORGY and some case studies mainly based on bioinformatics data