I am Professor of Trustworthy Software Technologies at Taltech. The position is a research measure of the IT Academy programme, funded by the Estonian State and the European Social Fund. I lead the Laboratory for Compositional Systems and Methods. In 2021-25 I am also PI of the Estonian Research Council grant PRG1210, Automata in Learning, Interaction and Concurrency (ALICE).
My research can be understood as the study of how to connect open systems (of various kinds: programs, networks, computing devices, circuits, ...) in a way that the description of the connections--i.e. the language that we describe subsystems and how to compose them---is compatible with the behaviour of the system. Therefore, what can be observed of the global system is entirely derivable from the observations made of the component subsystems. This is because each composition operation in the language we use for describing systems gives rise to an analogous operation on the behaviours. This property is known as compositionality.
I focus on compositional modelling of systems, developing the underlying mathematics (usually category theory), and applying it to real-life problems such as verification. I work on graph transformation, Petri nets, process algebras, dynamical and cyberphysical systems, as well as mainstream concurrent programming. Since 2015, I write the Graphical Linear Algebra blog about rediscovering linear algebra in a compositional way, with string diagrams.
- Upcoming meetings
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- 26th International Conference on Foundations of Software Science and Computation Structures (FoSSaCS 2023), co-chair (with Orna Kupferman), dates TBA, Paris, France
- Recent meetings
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- Eighth Symposium on Compositional Structures (SYCO 8), Tallinn, 13-14 December 2021
- Organiser, 46th International Symposium on Mathematical Foundations of Computer Science, Tallinn, Estonia, August 23-27, 2021
- Organisations
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- Member of Expert Panel on Computer Science and Informatics, National Science Centre NCN, Poland
- Associate Editor, Compositionality
- Associate Editor, Mathematical Structures in Computer Science, CUP
- IFIP Working Group 2.2, Formal Description of Programming Concepts
- IFIP Working Group 1.3, Foundations of System Specification
- ACM SigLOG
- Programme committees
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2023
- 38th Annual ACM/IEEE Symposium on Logic in Computer Science (LICS 2023)
- 16th International Conference on Graph Transformation (ICGT 2023)
2022
- 33rd International Conference on Concurrency Theory (CONCUR 2022)
- 19th International Conference on Quantum Physics and Logic (QPL 2022)
- 26th International Conference on Foundations of Software Science and Computation Structures (FoSSaCS 2023)
- 48th International Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM 2023)
- 9th Symposium on Compositional Structures (SYCO 9)
2021
- 32nd International Conference on Concurrency Theory (CONCUR 2021)
- 12th International Conference on the Theory and Application of Diagrams (Diagrams 2021)
- 30th EACSL Annual Conference on Computer Science Logic (CSL 2022)
- 25th International Conference on Foundations of Software Science and Computation Structures (FoSSaCS 2022)
- International Conference on Software Testing, Machine Learning and Complex Process Analysis, TMPA-2021
- Semantic Spaces at the Intersection of NLP, Physics and Cognitive Science (SEMSPACE 2021)
2020
- 35th Annual ACM/IEEE Symposium on Logic in Computer Science (LICS 2020)
- 17th International Conference on Quantum and Physics Logic (QPL 2020)
- 7th Symposium on Compositional Structures (SYCO 7)
- 3rd IFIP WG 1.8 International Conference on Topics in Theoretical Computer Science, Track B: Logic, Semantics, and Programming Theory (TTCS 2020)
- 13th International Conference on Graph Transformation (ICGT 2020)
- Semantic Spaces at the Intersection of NLP, Physics and Cognitive Science (SEMSPACE 2020)
2019
- 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019), Track B
- 44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019)
- Semantic Spaces at the Intersection of NLP, Physics and Cognitive Science 2019 (SEMSPACE 2019)
- Quantum Physics and Logic 2019 (QPL 2019)
- Applied Category Theory 2019 (ACT 2019)
- International Conference on Software Testing, Machine Learning and Complex Process Analysis (TMPA 2019)
- Third Workshop on String Diagrams in Computation, Logic and Physics (STRINGS 3)
- 6th Symposium on Compositional Structures (SYCO 6)
- PhD students
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2011-15 Owen Stephens, Compositional Specification and Reachability Checking of Net Systems, ECS, University of Southampton, with Julian Rathke 2012-15 Fabio Zanasi, Interacting Hopf Algebras: the Theory of Linear Systems, Ecole Normale Supérieure Lyon, with Filippo Bonchi 2016-20 Jens Seeber, IMT School for Advanced Studies Lucca, Logical Completeness for String Diagrams, IMT School for Advances Studies, Lucca, with Filippo Bonchi 2018- Paul Wilson, ECS, with Fabio Zanasi 2019- Nathan Haydon, TTU 2019- Chad Nester, TTU 2019- Elena di Lavore, TTU 2019- Mario Román, TTU 2020- Matt Earnshaw, TTU 2020- Diana Kessler, TTU, with Amar Hadzihasanovic - Publications
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- , "High-level axioms for graphical linear algebra", In Science of Computer Programming, vol. 218, pp. 102791, 2022.
- , "String Diagram Rewrite Theory I: Rewriting with Frobenius Structure", In J. ACM, vol. 69, no. 2, pp. 14:1–14:58, 2022.
- , "Functorial Semantics for Partial Theories", In 48th ACM SIGPLAN Symposium on Principles of Programming Languages (POPL 2021), 2021.
- , "Compositional modelling of network games", In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021), 2021.
- , "A Survey of Compositional Signal Flow Theory", Chapter in Advancing Research in Information and Communication Technology - IFIP's Exciting First 60+ Years, Views from the Technical Committees and Working Groups (Michael Goedicke, Erich J. Neuhold, Kai Rannenberg, eds.), Springer, vol. 600, pp. 29–56, 2021.
- , "Bialgebraic foundations for the operational semantics of string diagrams", In Inf. Comput., vol. 281, pp. 104767, 2021.
- , "Diagrammatic Polyhedral Algebra", In 41st IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science, FSTTCS 2021, December 15-17, 2021, Virtual Conference (Mikolaj Bojanczyk, Chandra Chekuri, eds.), Schloss Dagstuhl - Leibniz-Zentrum für Informatik, vol. 213, pp. 40:1–40:18, 2021.
- , "A Canonical Algebra of Open Transition Systems", In Formal Aspects of Component Software - 17th International Conference, FACS 2021, Virtual Event, October 28-29, 2021, Proceedings (Gwen Salaün, Anton Wijs, eds.), Springer, vol. 13077, pp. 63–81, 2021.
- , "On Doctrines and Cartesian Bicategories", In 9th Conference on Algebra and Coalgebra in Computer Science, CALCO 2021, August 31 to September 3, 2021, Salzburg, Austria (Fabio Gadducci, Alexandra Silva, eds.), Schloss Dagstuhl - Leibniz-Zentrum für Informatik, vol. 211, pp. 10:1–10:17, 2021.
- , "Calculational Proofs in Relational Graphical Linear Algebra", In 23rd Brazilian Symposium on Formal Methods (SBMF 2020), 2020.
- , "Compositional Diagrammatic First-Order Logic", In 11th International Conference on the Theory and Application of Diagrams (DIAGRAMS 2020), 2020.
- , "Rule Algebras for Adhesive Categories", In Log. Methods Comput. Sci., vol. 16, no. 3, 2020.
- , "Contextual Equivalence for Signal Flow Graphs", In 23rd International Conference on Foundations of Software Science and Computation Structures (FoSSaCS 2020), Springer, vol. 12077, pp. 77–96, 2020.
- , "CARTOGRAPHER: a tool for string diagrammatic reasoning", In 8th Conference on Algebra and Coalgebra in Computer Science (CALCO 2019), 2019.
- , "Bialgebraic Semantics for String Diagrams", In 30th International Conference on Concurrency Theory, (CONCUR 2019), pp. 37:1–37:17, 2019.
- , "The Axiom of Choice in Cartesian Bicategories", In 8th Conference on Algebra and Coalgebra in Computer Science (CALCO 2019), 2019.
- , "Graphical Affine Algebra", In ACM/IEEE Symposium on Logic and Computer Science (LiCS `19), 2019.
- , "Diagrammatic Algebra: From Linear to Concurrent Systems", In 46th ACM SIGPLAN Symposium on Principles of Programming Languages (POPL 2019), 2019.
- , "Monoidal multiplexing", In 15th International Colloqium on Theoretical Aspects of Computing, 2018.
- , "Rewriting with Frobenius", In Proceedings of the 33rd Annual ACM/IEEE Symposium on Logic in Computer Science (LICS 2018), Oxford, UK, July 09-12, 2018, pp. 165–174, 2018.
- , "Graphical Conjunctive Queries", In Computer Science Logic 2018 (CSL 2018), 2018.
- , "Rule Algebras for Adhesive Categories", In Computer Science Logic 2018 (CSL 2018), 2018.
- , "Functorial Semantics for Relational Theories", In arXiv preprint arXiv:1711.08699, 2017.
- , "Refinement for signal flow graphs", In Concurrency Theory - 28th International Conference, (CONCUR 2017), 2017.
- , "Confluence of Graph Rewriting with Interfaces", In European Symposium on Programming (ESOP 2017), 2017.
- , "A categorical approach to open and interconnected dynamical systems", In Thirty-first annual ACM/IEEE symposium on Logic and Computer Science (LICS `16), 2016.
- , "Lawvere theories as composed PROPs", In 13th International Workshop on Coalgebraic Methods in Computer Science (CMCS `16), 2016.
- , "Rewriting modulo symmetric monoidal structure", In Thirty-first annual ACM/IEEE symposium on Logic and Computer Science (LICS `16), 2016.
- , "Towards Compositional Graph Theory", In MFPS XXXI, 2015.
- , "The Calculus of Signal Flow Diagrams I: Linear Relations on Streams", 2015.
- , "Full Abstraction for Signal Flow Graphs", In Principles of Programming Languages, POPL`15., 2015.
- , "A Programming Language for Spatial Distribution of Net Systems", In Petri Nets `14, 2014.
- , "Compositional Reachability in Petri Nets", In Reachability Problems, 2014.
- , "Transformation and Refinement of Rigid Structures", In ICGT`14, 2014.
- , "A Categorical Semantics of Signal Flow Graphs", In CONCUR`14, 2014.
- , "Interacting Hopf Algebras", Technical report, arXiv:1403.7048, 2014.
- , "Interacting Bialgebras are Frobenius", In FoSSaCS `14, 2014.
- , "Decomposing Petri nets", 2013.
- , "Relational Presheaves, Change of Base and Weak Simulation", In JCSS, 2013.
- , "Nets, relations and linking diagrams", In Algebra and Coalgebra in Computer Science (CALCO `13), 2013.
- , "Reachability via compositionality in Petri nets", 2013.
- , "Connector Algebras for C/E and P/T Nets' Interactions", In Log. Meth. Comput. Sci., 2013.
- , "Relational presheaves as labelled transition systems", In Coalgebraic Methods in Computer Science (CMCS `12), Springer, vol. 7399, pp. 40-50, 2012.
- , "Processes and Unfoldings: Concurrent Computations in Adhesive Categories", 2012.
- , "WiCcA: LTS generation tool for wire calculus", In Algebra and Coalgebra in Computer Science (CALCO Tools `11), Springer, vol. 6859, pp. 407–412, 2011.
- , "Being Van Kampen is a universal property", In Log. Meth. Comput. Sci., vol. 7, no. 1, 2011.
- , "Adhesivitiy is not enough: Local Church-Rosser revisited", In Mathematical Foundations of Computer Science (MFCS `11), Springer, vol. 6907, pp. 48–59, 2011.
- , "Representations of Petri net interactions", In Concurrency Theory (CONCUR `10), Springer, no. 6269, pp. 554–568, 2010.
- , "Deriving structural labelled transitions for mobile ambients", In Information and Computation, vol. 208, pp. 1221-1242, 2010.
- , "A non-interleaving process calculus for multi-party synchronisation", In ICE '09, 2009.
- , "Making the unobservable, unobservable", In Proceedings of ICE '08, vol. 229, no. 3, pp. 131–144, 2009.
- , "Van Kampen colimits as bicolimits in Span", In Algebra and Coalgebra in Computer Science (Calco '09), Springer, no. 5728, pp. 335–349, 2009.
- , "Foreword: Festschrift for Mogens Nielsen's 60th birthday", In Theor. Comput. Sci., vol. 410, no. 41, pp. 4001–4005, 2009.
- , "Unfolding grammars in adhesive categories", In Algebra and Coalgebra in Computer Science (Calco '09), Springer, no. 5728, pp. 350–366, 2009.
- , "Subobject transformation systems", In Applied Categorical Structures, Kluwer, vol. 16, no. 3, pp. 389–419, 2008.
- , "Deconstructing behavioural theories of mobility", In Fifth IFIP International Conference On Theoretical Computer Science - TCS '08, Springer, 2008.
- , "Deriving structural labelled transitions for mobile ambients", In Concurrency Theory (CONCUR `08), Springer, vol. 5201, pp. 462–476, 2008.
- , "Quasitoposes, quasiadhesive categories and Artin glueing", In Algebra and Coalgebra in Computer Science, Calco '07, Springer, vol. 4626, 2007.
- , "Semantic barbs and biorthogonality", In Foundations of Software Science and Computation Structures, FoSSaCS '07, Springer, vol. 4423, pp. 302–316, 2007.
- , "Toposes are adhesive", In International conference on graph transformation, ICGT '06, Springer, vol. 4178, pp. 184–198, 2006.
- , "Reversing graph transformations", In Workshop on Petri nets and graph transformations, PNGT '06, vol. 2 (2006), 2006.
- , "General reversibility", In International Workshop on Expressiveness in Concurrency, Express '06, Elsevier, 2006.
- , "Processes for Adhesive Rewriting Systems", In Foundations of Software Science and Computation Structures, FoSSaCS '06, Springer, vol. 3921, pp. 202–216, 2006.
- , "Locating reaction with 2-categories", In Theoretical Computer Science, vol. 333, no. 1-2, pp. 297–327, 2005.
- , "A congruence for Petri nets", In Workshop on Petri nets and graph transformation, PNGT '04, Elsevier, vol. 127, pp. 107–120, 2005.
- , "Reactive Systems over Cospans", In Logic in Computer Science, LiCS '05, IEEE Press, pp. 311–320, 2005.
- , "Deriving weak bisimulation congruences from reduction systems", In International Conference on Concurrency Theory, Concur '05, Springer, vol. 3653, pp. 293–307, 2005.
- , "Labels from reductions: towards a general theory", In Algebra and Coalgebra in Computer Science, Calco '05, Springer, vol. 3629, pp. 30–50, 2005.
- , "Adhesive and quasiadhesive categories", In RAIRO - Theoretical Informatics and Applications, EDP Sciences, vol. 39, no. 2, pp. 522–546, 2005.
- , "Deriving process congruences from reaction rules", PhD thesis, BRICS, University of Aarhus, 2004.
- , "Process congruences from reaction rules (Luca Aceto's Concurrency Column)", In Bulletin of the EATCS, vol. 84, 2004.
- , "Adhesivity, bigraphs and bisimulation congruence", In Dagstuhl Seminar 04241, Graph Transformations and Process Algebras for Modeling Distributed and Mobile Systems, 2004.
- , "Adhesive categories", In Foundations of Software Science and Computation Structures, FoSSaCS '04, Springer, vol. 2987, pp. 273–288, 2004.
- , "Deriving Bisimulation Congruences Using 2-categories", In Nordic Journal of Computing, vol. 10, no. 2, pp. 163–183, 2003.
- , "Deriving bisimulation congruences: 2-categories vs precategories", In Foundations of Software Science and Computation Structures, FoSSaCS '03, Springer, vol. 2620, 2003.
- , "Syntactic Formats for Free: An Abstract Approach to Process Equivalence", In International Conference on Concurrency Theory, Concur '03, Springer, vol. 2620, pp. 72–86, 2003.
- , "Deriving Bisimulation Congruences: A 2-categorical Approach", In International Workshop on Expressiveness in Concurrency, Express '02, Elsevier, vol. 68, no. 2, 2002.
- , "High-level axioms for graphical linear algebra", In Science of Computer Programming, vol. 218, pp. 102791, 2022.