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

December 13, 2023: Our proposal to run the GRADES-NDA workshop at the ACM SIGMOD conference next year has been accepted, and so has our proposal to organize the 2nd International Workshop on Data Management for Knowledge Graphs (DMKG) at the 21st ESWC Conference in May 2024.

November 29, 2023: I have been selected for the prestigious Wallenberg Academy Fellows program of the Knut and Alice Wallenberg Foundation!!! There is a PDF file press release of the Foundation and a brief presentation of all the fellows selected in 2023, including the one about me. Linköping University also has a news item about the fellowship.

November 23, 2023: New journal article: With our earlier PhD student Huanyu Li and colleagues Rickard Armiento and Patrick Lambrix we have received the notification that our article titled "Ontology-Based GraphQL Server Generation for Data Access and Data" has finally been accepted for publication in the Semantic Web Journal (by IOS Press). While the publisher's version is being prepared, we have already made available the PDF file camera-ready version of the manuscript. Additionally, you may look at the Github repo of OBG-gen, including the material of the evaluation.

November 1, 2023: Best paper award!! The paper "Considering Vocabulary Mappings in Query Plans for Federations of RDF Data Sources" that I co-authored with my PhD student Sijin Cheng and earlier postdoc Sebastian Ferrada was honored with the best paper award at the 29th International Conference on Cooperative Information Systems (CoopIS). We have made available the PDF file camera-ready version of this paper.

October 16, 2023: I have been invited to give a keynote in the 7th Workshop on Storing, Querying and Benchmarking Knowledge Graphs (QuWeDa) at ISWC 2023.

September 20, 2023: New paper: With my PhD student Shahrzad Khayatbashi and colleague Amin Jalali (Stockholm University) we have a paper titled "Transforming Event Knowledge Graph to Object-Centric Event Logs: A Comparative Study for Multi-dimensional Process Analysis" at ER 2023. We have made available the PDF file camera-ready version of this paper. Additionally, you may look at the Github repo with an implementation of the transformation defined in the paper.

August 14, 2023: New paper: With my PhD student Sijin Cheng and earlier postdoc Sebastian Ferrada we have a paper titled "Considering Vocabulary Mappings in Query Plans for Federations of RDF Data Sources" at CoopIS 2023. We have made available the PDF file camera-ready version of this paper.

July 15, 2023: New paper: With colleagues of the Distributed Data Management group at the University of Nantes we have a paper titled "FedShop: A Benchmark for Testing the Scalability of SPARQL Federation Engines" at ISWC 2023. We have made available the PDF file camera-ready version of this paper. Additionally, you may look at the Github repo for FedShop.

July 5, 2023: I will serve as In-Use Track co-chair of the 21st Extended Semantic Web Conference (ESWC), which will take place in May 2024 in Hersonissou, Greece.

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.

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