The GReTA Graph TRansformation Theory and Applications virtual seminar series aims to serve as a platform for the international graph rewriting community, promote recent developments and trends in the field, and permit 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).

If you wish to contribute a talk to the GReTA seminar, please communicate this by filling out this online form.

Several options are available to receive regular updates on the GReTA seminars:

Upcoming Seminars

A graphical language for programming with graph rewriting
We provide a general introduction to the AlgebraicJulia ecosystem and AlgebraicRewriting.jl, which allows for integrating general-purpose code with computation of many graph transformation constructions in a broad variety of categories. Practical applications of graph transformation depend on being able to apply sequences of rewrites in a controlled manner: we present work on a graphical language for the construction and composition of such programs, including computation of normal forms as well as scientific agent-based model simulations. This graphical language can be given semantics in many different contexts (e.g. deterministic, nondeterministic, probabilistic) and can be functorially migrated, which yields graph rewriting programs that operate in other categories.

Previous Seminars

★★★ GReTA Special Event ★★★ Graph Rewriting as a Foundation for Science and Technology (and the Universe)
Stephen Wolfram is the creator of Mathematica, Wolfram|Alpha and the Wolfram Language; the author of A New Kind of Science; the originator of the Wolfram Physics Project; and the founder and CEO of Wolfram Research. Over the course of more than four decades, he has been a pioneer in the development and application of computational thinking—and has been responsible for many discoveries, inventions and innovations in science, technology and business.

Source: About Stephen Wolfram
Visual Smart Contracts for DAML: A Case Study in Groove
The Digital Asset Modelling Language (DAML) enables low-code development of smart contract applications. Starting from a high-level but textual notation, DAML thus implements the lower end of a model-driven development process, from a platform-specific level to implementations on a range of blockchain platforms. We develop a notation based on class diagrams and visual contracts that map directly to DAML smart contracts. The approach supports an operational semantics in terms of graph transformation systems to capture the complex behavioural features of DAML, such as its role-based access control and the order of contract execution and archival. We use the Doodle case study from a DAML tutorial to introduce the mappings between DAML, visual models, and operational semantics. To implement, explore and analyse the operational semantics of the case study we present the graph transformation tool Groove, originally developed by Arend Rensink and his students to support the verification of object-oriented programs. It has since been employed to analyse a range of models, for P2P networks, workflows, component configurations, etc. Our use of Groove for the semantic underpinning and analysis of DAML follows its original purpose of program verification. We will use the opportunity to discuss Groove’s features and illustrate its use for creating and analysing graph transformation systems.
Activation diagrams as a tool for generating consistency-preserving graph transformation rules: the case of product-line configuration with Acapulco
Graph transformations that change a graph while preserving consistency wrt a given set of constraints are an important type of transformation in many areas. For example, in search-based optimisation over graphs, aiming to find graph structures (e.g., models) that are optimal wrt some given objective functions, we need to be able to make changes to a graph without introducing violations of consistency constraints so that we can ensure to only generate feasible solutions. However, writing graph-transformation rules that ensure consistency-preservation while still allowing change to the graph is difficult: A change to the graph may introduce a constraint violation and, therefore, the rule must include components that repair any such new violations. Any such repair has the potential to introduce new constraint violations itself and, therefore, the number of potential repair paths to follow can quickly explode exponentially in size. In this talk, I present work addressing these challenges in the context of optimal product-line configuration. We introduce a new data structure – feature-activation diagrams – to capture the dependencies between changes and use this to efficiently derive consistency-preserving graph transformation rules encoded as variability-based rules. The rules we generate allow us to solve existing benchmarks for product-line configuration more efficiently than the state of the art and find more optimal configurations.
Comprehensive Systems for Software Interoperability Problems
Software interoperability is a recurring issue in nearly every bigger software project where two or more (legacy) software systems are involved. One aspect of interoperability, that is considered especially tricky is semantic interoperability, i.e., aligning the concepts, entities, data structures from multiple systems with each other. The model-driven software engineering community has investigated this issue under different names: model management, model synchronisation, inter-model consistency. From a theoretical side, there are two noteworthy common approaches: Goguen’s Colimit-approach (for general systems' theory) and Triple Graph Grammars (TGGs). The former describes that idea that one may always consider a “global integrated system” as the colimit of a diagram of interacting systems, while the latter is the foundation for a powerful framework of binary model synchronizers derived from a declarative description (grammar). In our investigation, it, however, turned out that both approaches each have significant drawback when considering them in practical applications: The colimit turns out to be a “forgetful” operation and TGGs are limited to a binary setting (it is a well-known fact from logic and databases that there are multi-ary relations that cannot be factored into a system of binary relations). Thus, we invented a novel formalism, called comprehensive systems, first introduced in 1, and theoretically flashed out in 2 and 3. Comprehensive systems provide an alternative to the colimit approach, which can be thought of as instead of “merging” a diagram into a singular object, they “flatten” the whole diagram. Moreover, they are designed for a general n-ary ($n \geq 2$) settings and thus can be considered as a generalization of triple graphs. In a series of papers, we have shown that comprehensive systems admit SPO and DPO rewriting in the setting of a weak adhesive HLR category. From a practical perspective, comprehensive systems serve as the theoretical foundation of a prototypical software interoperability tool called CorrLang.
In this talk, I will provide a brief historical overview over interoperability, model management, and model synchronisation, provide the motivation for comprehensive systems, sketch their theoretical properties (with an emphasis on partial morphisms), and, if time allows, demonstrate how comprehensive systems are reified in a concrete tool (CorrLang).

How to participate

The GReTA seminars are hosted via Zoom. For security reasons, participation in a given seminar requires a registration (via the link provided in the seminar announcement). Upon completing the registration form (asking for the name, affiliation, and email address), you will be sent a personalized Zoom meeting link. For convenience, sessions will be open 15 minutes before the beginning of the seminar.

Please make sure that you have the latest Zoom client version installed, in particular if you wish to participate in the after-talk discussions (since these will make use of the breakout rooms feature, see here for usage instructions). If possible, please consider joining already during the 15 minutes before a given seminar, ensuring your Zoom setup is functioning correctly.

Alternatively, if you prefer not to participate via Zoom, some seminars will be live-streamed to YouTube, where it will be possible to ask questions via the YouTube commenting functionality.

Seminar “etiquette”

Each seminar will be hosted by a chairperson who will introduce the speaker, watch incoming questions and who will decide if and when to interrupt the speaker for questions, or which questions should be postponed to after the talk.

After-seminar discussions

After each seminar, the main Zoom session will remain open for additional 30 minutes in order to allow for discussions and networking. Depending on the number of participants, it will be a possibility to gather into small breakout sessions as well.

Meet the GReTA Team

Organisers

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Andrea Corradini

Professor of Computer Science

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Reiko Heckel

Professor in Software Engineering

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Nicolas Behr

CNRS Researcher in Computer Science

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Jean Krivine

CNRS Researcher in Computer Science

Scientific Committee

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Barbara König

Professor of Computer Science

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Berthold Hoffmann

Bremen Senior Lecturer (emer.)

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Daniel Merkle

Professor of Computer Science

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Dan R. Ghica

Professor of Semantics of Programming Languages

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Detlef Plump

Associate Professor of Computer Science

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Eswaran Subrahmanian

Research Professor

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Fabio Gadducci

Professor of Computer Science

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Fernando Orejas

Professor of Computer Science

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Frank Drewes

Professor of Computer Science

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Gabriele Taentzer

Professor of Computer Science

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Hans-Jörg Kreowski

Professor in Computer Science (emer.)

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Jérôme Feret

Research fellow at INRIA

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Leen Lambers

Professor of Computer Science

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Maribel Fernandez

Professor in Computer Science

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Mark Minas

Professor of Computer Science

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Matthias Tichy

Professor in Software Engineering

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Paolo Bottoni

Professor of Computer Science

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Paolo Baldan

Associate Professor of Computer Science

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Paweł Sobociński

Professor of Trustworthy Software Technologies

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Rachid Echahed

CNRS Researcher in Computer Science

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Russ Harmer

CNRS Researcher in Computer Science

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Timo Kehrer

Professor of Computer Science

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Vincent Danos

Professor, Directeur de Recherches at CNRS

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Steffen Zschaler

Reader in Computer Science