Research Interests

I am interested in problems related to the management of databases and knowledge. My focus in this broad context is on data on the Web (Semantic Web and Linked Data, in particular) and on graph data, as well as on problems in which the data is distributed over multiple, autonomous and/or heterogeneous sources (keywords: federated data management, federated knowledge graphs). Other keywords that appear in some of my work are data provenance and data quality. Regarding all of these topics, my interests range from theoretical foundations (e.g., complexity and expressive power of query languages) all the way to systems-building related research (e.g., efficient storage of datasets and databases, query processing, and query optimization).

News

May 15, 2023: New paper: With my PhD student Sijin Cheng we have a paper titled "A Cost Model to Optimize Queries over Heterogeneous Federations of RDF Data Sources" at the Data Management for Knowledge Graphs workshop (DMKG) at ESWC 2023. We have made available the PDF file camera-ready version of this paper.

February 22, 2023: I have been invited to deliver a seminar at the Belgian Scientific Research Network on Knowledge Graphs For Data Integration.

December 20, 2022: Our proposal to run the 1st International Workshop on Data Management for Knowledge Graphs (DMKG) at the 20th ESWC Conference in May 2023 has been accepted.

December 6, 2022: I will serve as co-organizer of the GRADES-NDA workshop at the ACM SIGMOD conference next year.

October 31, 2022: According to my Google Scholar profile, I have reached a total of 4000 citations for my publications!

October 17, 2022: New paper: With my PhD student Sijin Cheng we have a paper titled "Source Selection for SPARQL Endpoints: Fit for Heterogeneous Federations of RDF Data Sources?" at the QuWeDa Workshop at ISWC 2022. We have made available the PDF file camera-ready version of this paper.

September 26, 2022: Our vision paper "The OneGraph Vision: Challenges of Breaking the Graph Model Lock-In" has been accepted by the Semantic Web Journal and will appear in 2023 in volume 14 of the journal. In the meantime, you can already read the PDF file camera-ready version of this paper.

September 13, 2022: I gave a keynote titled "Towards Querying Heterogeneous Federations of Interlinked Knowledge Graphs" at the 18th SEMANTiCS conference in Vienna. The PDF file slides are available for download.

CV

Here is my academic CV: PDF file

Selected Publications

This following list contains selected publications. There is also a complete list of all my publications.

Olaf Hartig and Jorge Pérez: Semantics and Complexity of GraphQL. In Proceedings of The Web Conference 2018 (27th International World Wide Web Conference), Lyon, France, Apr. 2018
Olaf Hartig, Ian Letter, and Jorge Pérez: A Formal Framework for Comparing Linked Data Fragments. In Proceedings of the 16th International Semantic Web Conference (ISWC), Vienna, Austria, Oct. 2017 (Best Paper Award winner)
Olaf Hartig and Jorge Pérez: LDQL: A Query Language for the Web of Linked Data. In Journal of Web Semantics 41, pages 9-29 Dec. 2016 (Notice, the linked PDF is a pre-print. The final publication is available at www.sciencedirect.com.)
Olaf Hartig: SPARQL for a Web of Linked Data: Semantics and Computability. In Proceedings of the 9th Extended Semantic Web Conference (ESWC), Heraklion, Greece, May 2012 ... Extended Version in CoRR (abs/1203.1569)
Olaf Hartig, Christian Bizer, and Johann-Christoph Freytag: Executing SPARQL Queries over the Web of Linked Data. In Proceedings of the 8th International Semantic Web Conference (ISWC), Washington, DC, USA, Oct. 2009 (SWSA 10-Year Award winner in ISWC 2019)
Olaf Hartig: Querying Trust in RDF Data with tSPARQL. In Proceedings of the 6th European Semantic Web Conference (ESWC), Heraklion, Greece, Jun. 2009 (Best Paper Award winner)

Get in Touch

EMail Address:

Office: Building B, Ground floor, Room 2B:478

Postal address: Dept. of Computer and Information Science (IDA), Linköpings universitet, SE-581 83 Linköping, SWEDEN