Publications related to HeFQUIN

Sijin Cheng and Olaf Hartig: FedQPL: A Language for Logical Query Plans over Heterogeneous Federations of RDF Data Sources. In Proceedings of the 22nd International Conference on Information Integration and Web-based Applications & Services (iiWAS), 2020.

This paper introduces a formal language for describing and optimizing the logical plans used by an RDF query federation engine. The operators of that language are indeed the basis for the logical plans in HeFQUIN (which you find in the 'se.liu.ida.hefquin.engine.queryplan.logical.impl' Java package).

Sijin Cheng and Olaf Hartig: Source Selection for SPARQL Endpoints: Fit for Heterogeneous Federations of RDF Data Sources?. In Proceedings of the 6th Workshop on Storing, Querying and Benchmarking Knowledge Graphs (QuWeDa), 2022.

Sijin Cheng and Olaf Hartig: A Cost Model to Optimize Queries over Heterogeneous Federations of RDF Data Sources. In Proceedings of the 1st International Workshop on Data Management for Knowledge Graphs (DMKG), 2023.

This paper introduces an initial cost model for deciding on the physical plans (mainly the join order and the join algorithms to be selected). While this cost model is implemented in HeFQUIN, it is disabled by default because we are planning to refactor it. More generally, there is still a lot that can (and needs to be) done regarding cost-based query optimization, both in HeFQUIN and also in terms of research. Nonetheless, the paper was our first step in this direction for HeFQUIN.

Sijin Cheng, Sebastian Ferrada, and Olaf Hartig: Considering Vocabulary Mappings in Query Plans for Federations of RDF Data Sources. In Proceedings of the 29th International Conference on Cooperative Information Systems (CoopIS), 2023.

This paper is about considering vocabulary mappings when planning and executing SPARQL queries over a federation. This approach is implemented in HeFQUIN as well, but so far not really covered in the documentation.

Sitt Min Oo and Olaf Hartig: An Algebraic Foundation for Knowledge Graph Construction. In Proceedings of the 22nd European Semantic Web Conference (ESWC), 2025.

Olaf Hartig and Jonas Westman: Querying Federations of SPARQL Endpoints and JSON-based Web APIs with HeFQUIN. In Proceedings of Satellite Events of the 23rd European Semantic Web Conference (ESWC), 2026.

Olaf Hartig: The HeFQUIN Approach to Extract and to Process Composite Values with RML and SPARQL. In Proceedings of the 7th International Workshop on Knowledge Graph Construction (KGCW), 2026.