Author: Olaf Hartig

Associate Professor in Computer Science with an interest in topics related to data management; in particular, Web data and graph data.
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LiU Semantic Web research at The Web Conference 2018

Next week, the 27th edition of The Web Conference (earlier called International World Wide Web Conference – WWW) will take place in Lyon, France, and different results of Semantic Web research at LiU will be present at the conference.

First, there is a research paper in the main research track of the conference by our Olaf Hartig and Jorge Pérez from the Universidad de Chile. The title of the paper is “Semantics and Complexity of GraphQL.”

Additionally, Olaf will give an invited talk in the Web Stream Processing workshop at the conference. While the exact title of the talk is yet to be decided, the talk will present recent work about the RDF*/SPARQL* Approach to Statement-Level Metadata in RDF.

Find Olaf and talk to him if you also happen to be in the conference; he will be happy to tell you more about his research, as well as our other Semantic Web related research at LiU.

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A very successful ISWC 2017 for LiU SemWeb

Many of us attended the 16th International Semantic Web Conference (ISWC) which was held on October 21-25 in the beautiful city of Vienna, and it turned out to be a very successful conference for us! Our contributions to the conference were in the co-organization of workshops (WOP 2017 and VOILA 2017), a tutorial (“Semantic Data Management in Practice”) and two tracks of the Ontology Alignment Evaluation Initiative, as well as two research papers (“Alignment Cubes: Towards Interactive Visual Exploration and Evaluation of Multiple Ontology Alignments” and “A Formal Framework for Comparing Linked Data Fragments”), a demo, and a poster. In addition to successfully running our aforementioned sub-events and presenting our research, we won a couple of awards:

  • Valentina won a best reviewer award for the main research track,
  • Olaf won the peoples’ choice best poster award, and
  • together with Ian Letter and Jorge Pérez (both from the Universidad de Chile), Olaf also won the best research paper award! You may want to read a brief description of this work.

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Zlatan Dragisic defended his PhD Thesis on Completion of Ontologies and Ontology Networks

Yesterday, on September 26, our PhD candidate Zlatan Dragisic defended successfully his thesis with the title “Completion of Ontologies and Ontology Networks.” The thesis makes several contributions: First, the problem of completing the is-a structure in ontologies is formalized as an abductive reasoning problem and the thesis introduces algorithms as well as systems for dealing with the problem. Regarding the completion of alignments between ontologies, the thesis provides a performance study of systems that participated in the Ontology Alignment Evaluation Initiative, and an approach to reduce the search space when generating such alignments. Next, the thesis reports a broad study of state-of-the-art ontology alignment systems in terms of user involvement during the completion process and, in particular, the impact of user errors in this process. Finally, the thesis introduces an approach to integrate ontology completion and ontology alignment into an existing ontology development methodology.

Zlatan’s work on the thesis was supervised by Patrick Lambrix, and co-supervised by Nahid Shahmehri, Marco Kuhlmann, and Fang Wei-Kleiner. The opponent was Erhard Rahm from the University of Leipzig, Germany. The examination committee consisted of Asuncion Gomez-Perez from Universidad Politecnica de Madrid, Jerome Euzenat from INRIA and Graham Kemp from Chalmers University of Technology. Magnus Bång from Linköping University was backup examination committee member.

Find the thesis in the Diva portal.

Well done Zlatan! Congratulations!

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Emanuele Della Valle (Politecnico di Milano) will talk at LiU about Stream Reasoning

On October 5 (Thursday), Emanuele Della Valle of Politecnico di Milano, Italy, will give a Semantic Web related talk at LiU. The title of his talk is:

Stream Reasoning: A Summary of Ten Years of Research and a Vision for the Next Decade

Abstract: Stream reasoning studies the application of inference techniques to data characterised by being highly dynamic. It can find application in several settings, from Smart Cities to Industry 4.0, from Internet of Things to Social Media analytics. This year stream reasoning turns ten, and this talk analyses its growth. In the first part, it traces the main results obtained so far, by presenting the most prominent studies. It starts by an overview of the most relevant studies developed in the context of semantic web, and then it extends the analysis to include contributions from adjacent areas, such as database and artificial intelligence. Looking at the past is useful to prepare for the future: the second part presents a set of open challenges and issues that stream reasoning will face in the next future.

Time and date: 9.00am, October 5, 2017

Location: Campus Valla, Building E, Room “Alan Turing”

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Dagstuhl seminar on Federated Semantic Data Management

During the last week of June, I co-organized a Dagstuhl seminar on Federated Semantic Data Management together with Maria-Esther Vidal and Johann-Christoph Freytag. It was a very intense week with a packed schedule and almost no time to catch some breath (exactly like how a Dagstuhl seminar should be I guess 😉

To start with, we had scheduled a few short, survey-style talks on a number of topics related to the seminar. In particular, these talks covered:

While these talks were meant to establish a common understanding of key concepts and terminology, the major focus of the seminar was on discussions and working groups. To this end, we had invited a good mix of participants from the Semantic Web field, from Databases, as well as from application areas. Due to this mix, we ended up on several occasions and in different constellations discussing and reflecting in depth the fundamental assumptions and the core ideas of federated semantic data management. These general discussions and reflections kept re-emerging not only during the sessions, but also during the meals, the coffee breaks, and the evenings in Dagstuhl’s wine cellar. In my opinion, clearly articulating and repeatedly arguing about these assumptions and ideas was a long-needed discussion to be had in the community. After this week, I would guess that many of the participants have a much clearer understanding of what federated semantic data management can and should be, and I am certain that this understanding will be reflected in the reports that the working groups are preparing.

Speaking of working groups, the seminar was structured around four topics addressed by four separate working groups who came together occasionally to report on their progress and obtain feedback from the other groups. The topics were:

  • RDF and graph data models
  • Federated query processing
  • Access control and privacy
  • Use cases and applications

Each of the working groups is currently preparing a summary of their discussions and results. These summaries will become part of our Dagstuhl report (to be published some time in August if all goes well). In addition to this report, we are planning to document the discussions and the results of the seminar in a collection of more detailed publications.

What’s next? We have some ideas to keep the momentum and to advance the discussions around the seminar topics in a more continuous community process. Stay tuned.

Olaf