Jelle Hellings

Jelle Hellings
Visiting Indiana University, Bloomington.

Postdoctoral researcher, Exploratory Systems Lab, Department of Computer Science, University of California, Davis, CA 95616-8562, USA.

Office:Kemper Hall, Room 3062

Research

My current research focusses on the usage of blockchain technologies in the construction of distributed database systems. Previously, I focused on data management and database theory, with the main focus on graph structured data. Topics I have worked on include data dependencies, external-memory data processing, graph-structured data models, the expressive power of graph query languages, query evaluation and optimization, and temporal data.

PhD dissertation and Master thesis.

PhD dissertation (dissertation, defense slides, project page)
On Tarski's Relation Algebra: querying trees and chains and the semi-join algebra. Hasselt University and transnational University of Limburg. Adviser: Marc Gyssens of the Databases and Theoretical Computer Science Research Group at Hasselt University.
Master thesis (report, local version, midterm presentation slides, final presentation slides, project page, poster)
Bisimulation partitioning and partition maintenance. Eindhoven University of Technology. Adviser: George H. L. Fletcher.

Journal papers

AMAI 2016 (local version; see also: FoIKS 2014)
Jelle Hellings, Marc Gyssens, Jan Paredaens, Yuqing Wu. Implication and axiomatization of functional and constant constraints. In: Annals of Mathematics and Artificial Intelligence, volume 76, pages 251--279. Springer, 2016. DOI: doi:10.1007/s10472-015-9473-7

Conference papers (peer-reviewed)

FoIKS 2018 (local version, slides, project page)
Jelle Hellings, Yuqing Wu, Marc Gyssens, Dirk Van Gucht. The power of Tarski's relation algebra on trees. In: 10th International Symposium on Foundations of Information and Knowledge Systems, pages 244--264. Springer, 2018. DOI: doi:10.1007/978-3-319-90050-6_14
FoIKS 2018 (local version, slides)
Jelle Hellings, Marc Gyssens, Dirk Van Gucht, Yuqing Wu. First-order definable counting-only queries. In: 10th International Symposium on Foundations of Information and Knowledge Systems, pages 225--243. Springer, 2018. DOI: doi:10.1007/978-3-319-90050-6_13
DBPL 2017 (local version, slides)
Jelle Hellings, Catherine L. Pilachowski, Dirk Van Gucht, Marc Gyssens, Yuqing Wu. From relation algebra to semi-join algebra: an approach for graph query optimization. In: Proceedings of the 16th International Symposium on Database Programming Languages, article 5. ACM, 2017. DOI: doi:10.1145/3122831.3122833
DBPL 2015 (local version, slides)
Jelle Hellings, Marc Gyssens, Yuqing Wu, Dirk Van Gucht, Jan Van den Bussche, Stijn Vansummeren, George H. L. Fletcher. Relative expressive power of downward fragments of navigational query languages on trees and chains. In: Proceedings of the 15th Symposium on Database Programming Languages, pages 59--68. ACM, 2015. DOIL: doi:10.1145/2815072.2815081
ICDT 2014 (local version, slides)
Jelle Hellings. Conjunctive Context-Free Path Queries. In: Proceedings of the 17th International Conference on Database Theory, pages 119--130. OpenProceedings, 2014. DOI: doi:10.5441/002/icdt.2014.15
FoIKS 2014 (local version, slides; see also: AMAI 2016)
Jelle Hellings, Marc Gyssens, Jan Paredaens, Yuqing Wu. Implication and Axiomatization of Functional Constraints on Patterns with an Application to the RDF Data Model. In: 8th International Symposium on Foundations of Information and Knowledge Systems, pages 250--269. Springer, 2014. DOI: doi:10.1007/978-3-319-04939-7_12
ICDT 2013 (local version, slides)
Jelle Hellings, Bart Kuijpers, Jan Van den Bussche, Xiaowang Zhang. Walk logic as a framework for path query languages on graph databases. In: Proceedings of the 16th International Conference on Database Theory, pages 117--128. ACM, 2013. DOI: doi:10.1145/2448496.2448512
SIGMOD 2012 (local version, slides, poster, technical report, project page)
Jelle Hellings, George H.L. Fletcher, Herman Haverkort. Efficient external-memory bisimulation on DAGs. In: Proceedings of the 2012 ACM SIGMOD International Conference on Management of Data, pages 553--564. ACM, 2012. DOI: doi:10.1145/2213836.2213899

Technical reports

(technical report; see also: DBPL 2015)
Jelle Hellings, Marc Gyssens, Yuqing Wu, Dirk Van Gucht, Jan Van den Bussche, Stijn Vansummeren, George H. L. Fletcher.. Comparing Downward Fragments of the Relational Calculus with Transitive Closure on Trees.
(technical report)
Jelle Hellings. Querying for Paths in Graphs using Context-Free Path Queries.

Presentations

DBDBD 2016 (slides, abstract)
Jelle Hellings. Graph query optimization using semi-join rewritings.
WOG 2013 (slides, abstract, short abstract)
Jelle Hellings. Path Querying on Graph Databases.
DBDBD 2011 (slides, abstract, project page)
Jelle Hellings. Efficient external-memory bisimulation on DAGs.

Teaching

I was previously a researcher and teaching assistant at Hasselt University. Over time, I have taught courses on programming in Python, programming in Java, algorithms and data structures, introductions to databases, theoretical aspects of databases, software development, and logic and set theory. I also supervise student software development and provide day-to-day supervision of bachelor and master thesis projects.