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Reiko Heckel
Jean Krivine

The GReTA – Graph TRansformation Theory and Applications virtual seminar series aims to serve as a platform for the international graph rewriting community, to promote recent developments and trends in the field, and to permit a regular networking and interaction between members of this community. Seminars are held twice a month in the form of Zoom sessions (some of which will be live-streamed to YouTube).

Please refer to GReTA homepage for further information on how to participate in this seminar via Zoom or via YouTube live streams.

Prochaines séances

Graph Transformation Theory and Applications
Vendredi 4 décembre 2020, 15 heures, (online)
Daniel Merkle & Jakob Lykke Andersen (Department of Mathematics and Computer Science, University of Southern Denmark, Odense, Denmark) Chemical Graph Transformation and Applications

Any computational method in chemistry must choose some level of precision in the modeling. One choice is made in the methods of quantum chemistry based on quantum field theory. While highly accurate, the methods are computationally very demanding, which restricts their practical use to single reactions of molecules of moderate size even when run on supercomputers. At the same time, most existing computational methods for systems chemistry and biology are formulated at the other abstraction extreme, in which the structure of molecules is represented either not at all or in a very rudimentary fashion that does not permit the tracking of individual atoms across a series of reactions.

In this talk, we present our on-going work on creating a practical modelling framework for chemistry based on Double Pushout graph transformation, and how it can be applied to analyse chemical systems. We will address important technical design decisions as well as the importance of methods inspired from Algorithm Engineering in order to reach the required efficiency of our implementation. We will present chemically relevant features that our framework provides (e.g. automatic atom tracing) as well as a set of chemical systems we investigated are currently investigating. If time allows we will discuss variations of graph transformation rule compositions and their chemical validity.

Zoom registration link:


Link to YouTube live stream:


Graph Transformation Theory and Applications
Vendredi 18 décembre 2020, 15 heures, (online)
Maribel Fernandez & Bruno Pinaud (King's College London, UK & Université de Bordeaux, France) Hierarchical port graphs & PORGY - port graph rewriting as a modelling tool

Graph rewriting systems are natural verification and validation tools: they provide visual, intuitive representations of complex systems while specifying the dynamic behaviour of the system in a formal way. In this talk we will describe the use of strategic port graph rewriting as a basis for the implementation of a visual modelling tool: PORGY. We will present attributed hierarchical port graphs (AHP) and a notion of strategic AHP-rewriting as a mechanism to model the behaviour of dynamic systems. The system modelled 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. In the second part of the talk, we describe PORGY and give examples of application in the areas of biochemistry, social networks and finance.

This is joint work with members of the PORGY team at Bordeaux and King’s College London.

Graph Transformation Theory and Applications
Vendredi 15 janvier 2021, 15 heures, (online)
Gabriele Taentzer (Fachbereich Mathematik und Informatik, Philipps-Universität Marburg, Germany) Non encore annoncé.

Graph Transformation Theory and Applications
Vendredi 29 janvier 2021, 15 heures, (online)
Leen Lambers & Fernando Orejas (Hasso-Plattner-Institut Potsdam, Germany & Technical University of Catalonia (UPC), Spain) Confluence of Graph Transformation

We will review old and new results about confluence of GTS, without and with application conditions.

Zoom registration link: TBA

Link to YouTube live stream: TBA

Graph Transformation Theory and Applications
Vendredi 12 février 2021, 15 heures, (online)
Steffen Zschaler (Department of Informatics, King's College London, UK) MDEOptimiser: Searching for optimal models with EMF and Henshin

An overview presentation of the work we have been doing over the past years on MDEOptimiser, a tool that uses evolutionary search over EMF models to solve multi-objective optimisation problems. Graph transformations are used to encode mutation operators, opening interesting opportunities for automatically generating domain-specific mutation operators.

Graph Transformation Theory and Applications
Vendredi 26 février 2021, 15 heures, (online)
Detlef Plump & Graham Campbell (University of York, UK & Newcastle University, UK) Fast Graph Programs

This will be an overview of our ongoing work on fast graph programs in the language GP 2. We will present programs which in some cases match the time complexity of graph algorithms in imperative languages. In other cases we need to assume that input graphs have a bounded degree, to reach the speed of conventional algorithms.

Graph Transformation Theory and Applications
Vendredi 12 mars 2021, 15 heures, (online)
Jean-Pierre Jouannaud (Laboratoire d'Informatique (LIX), École Polytechnique) Composition-based Graph Rewriting

Double Pushout (DPO) rewriting, the dominant model for graph rewriting, emerged in the early 70’s, strongly influenced at that time by graph grammars. Developed by Hartmut Ehrig and his many collaborators, graph rewriting was from the beginning based on category theory, with the major insight that the two basic rewriting constructions, namely matching and replacement, were intimately related to graph morphisms and their pushouts. A new model has emerged recently, so-called Composition based rewriting (Core), in which rewriting is based on a composition operator over directed rooted labelled graphs (drags), so that matching a drag G against a drag L amounts to compose L with some context drag C, and rewriting G with L → R to compose R with C. We will describe Core for drags before to relate it precisely to DPO and extend it to adhesive categories of graphs and beyond. We will also show how to define composition abstractly in any category of graphs satisfying appropriate properties among which adhesivity (wrt monomorphisms). Major differences between DPO and Core will be discussed.

Zoom registration link: TBA

Link to YouTube live stream: TBA

Séances passées

Année 2020

Graph Transformation Theory and Applications
Vendredi 20 novembre 2020, 15 heures, (online)
Barbara König (Fakultät für Ingenieurwissenschaften, Universität Duisburg-Essen, Germany) Graph Transformation Meets Logic

We review the integration of (first-order) logic respectively nested conditions into graph transformation. Conditions can serve various purposes: they can constrain graph rewriting, symbolically specify sets of graphs, be used in query languages and in verification (for instance in Hoare logic and for behavioural equivalence checking).

In the graph transformation community the formalism of nested graph conditions has emerged, that is, conditions which are equivalent to first-order logic, but directly integrate graphs and graph morphisms, in order to express constraints more succinctly.

In this talk we also explain how the notion of nested conditions can be lifted from graph transformation systems to the setting of reactive systems as defined by Leifer and Milner. It turns out that some constructions for graph transformation systems (such as computing weakest preconditions and strongest postconditions and showing local confluence by means of critical pair analysis) can be done quite elegantly in the more general setting.

video recording of the seminar on YouTube