Dagstuhl seminar on Federated Semantic Data Management

Postad i: Seminar den 12 July, 2017 av Olaf Hartig

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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.



LiU Semantic Web group at ESWC2017

Postad i: Conferences, Ontology Design Patterns den 2 June, 2017 av Eva Blomqvist

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This week a couple of us have been at ESWC2017 in Portoroz, Slovenia. Eva Blomqvist was the general chair of the conference this year, hence, this was the culmination of a whole year of hard work for her. Olaf Hartig is the proceedings chair (proceedings part 1 and 2). He could not attend the conference this year, but has done great job with the Springer proceedings, and the upcoming post-proceedings volume with poster and demo papers among other things. In addition to this, Karl Hammar, was one of the organisers of the Modular Ontology Modeling with Ontology Design Patterns tutorial, together with Pascal Hitzler, Adila A. Krisnadhi, Agnieszka Lawrynowicz and Monika Solanki. In particular, Karl ran the hands-on session with his tool for ODP-based modelling in WebProtégé (called XDP). Finally, Henrik Eriksson, presented our EU-funded project VALCRI in the project networking session, and in the poster session.

The overall conference was interesting as always, and included a lot of networking opportunities, as well as interesting work to take a closer look at. A quick summary of some of the major events:


Kevin Crosbie, from Ravenpack, the first keynote speaker talking about how to model events in order to use them for predicting financial markets. Very interesting talk, describing how Ravenpack work with their data products and apply technologies very similar to Semantic Web, although technically not using the W3C standards, such as RDF.


At the end of the first day, Aldo Gangemi chaired a panel about the future of academic publishing, discussing the challenges and opportunities that lie ahead. It is clear that something needs to be done about both the reviewing situation in our field, the open access issue, and we want more focus on “eating our own dog food”. The discussions were also related to the paper that later won the best student paper award, on Linked Data Notifications.


Second keynote speaker, John Sheridan, from the National Archives in the UK, described how the National Archives heavily rely on Semantic Web technologies and standards to solve their archiving tasks. However there are also challenges of course, which can hopefully be solved by working together: academia and society at large. Particularly interesting for us at LiU to hear that the National Archives is in great need of a better solution for modelling trust and uncertainty in their data, which could be a potential use case for the recent research results on RDF* and SPARQL* by Olaf Hartig.


Nice conference dinner at the beach, and a chance for the general chair to thank all the people in the organising committee.


Poster session with lots of interesting interactions and discussion, here with Diego Reforgirato, who later won both the best poster and best demo awards.

Unfortunately, we did not take any picture of the last keynote, Lora Aroyo, who gave a very interesting keynote on the last day. She started with an overview of the evolution of the field, pointing out that studying and using people to acquire knowledge has always been a central part of our research. However, by over simplifying, and trying to fit every answer into yes/no categories, we can introduce wrong conclusions. She means that we need to be aware of ambiguity and diversity in opinions, that there is usually not one true answer, and instead turn that to our advantage. Lora showed a vector-based model to represent diversity in opinions.

Finally, Aldo Gangemi will be the next general chair of ESWC in 2018, and he made a series of interesting promises for the next year, among others: double-open review process, improvements in the online pre-prints of the proceedings and the dataset, a resources track and an industry session á la ISWC, and better music in the social events. We all wish him the best of luck with the next conference, and we are excited to see all the innovations next year!


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Kim Ahlstrøm (Aalborg University) will talk in the LiU Semantic Web Seminars Series

Postad i: Seminar den 24 January, 2017 av Olaf Hartig

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KimAhlstromOn February 7 (Tuesday), Kim Ahlstrøm of Aalborg University will give a talk in our series of Semantic Web seminars. The title of his talk is:

Towards Answering Provenance-Enabled SPARQL Queries over RDF Data Cubes

Abstract: The SPARQL 1.1 standard has made it possible to formulate analytical queries in SPARQL. While some approaches have become available for processing analytical queries on RDF data cubes, little attention has been paid to answering provenance-enabled queries over such data. Yet, considering provenance is a prerequisite to being able to validate if a query result is trustworthy. The main challenge for existing triple stores is the way provenance can be encoded in standard triple stores based on context values (named graphs). In this talk, I will present shortcomings in existing techniques, and we propose an index to handle the high number of context values that provenance encoding typically entails. Our experimental results using the Star Schema Benchmark show the feasibility and scalability of our index and query evaluation strategies.

Time and date: 3.15pm, February 7, 2017

Location: Campus Valla, Building B, Room “Charles Babbage”


LiU Semantic Web research in Semantic Web Special issue on ontology and linked data matching

Postad i: Journal den 18 January, 2017 av Patrick Lambrix

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Two papers with co-authors from our group are published in a special issue on ontology and linked data matching of the Semantic Web journal:

Lambrix P, Kaliyaperumal R, A Session-based Ontology Alignment Approach enabling User Involvement, Semantic Web Journal, 8(2):225-251, 2017.

Zhang Z, Gentile A, Blomqvist E, Augenstein I, Ciravegna F, An unsupervised data-driven method to discover equivalent relations in large Linked Datasets, Semantic Web Journal, 8(2):197-223, 2017.


Marjan Alirezaie (Örebro University) will talk in the LiU Semantic Web Seminars Series

Postad i: Seminar den 17 January, 2017 av Olaf Hartig

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PhotoMarjanAlirezaieOn Tuesday next week, January 24, Marjan Alirezaie of Örebro University will give a talk in our series of Semantic Web seminars. The title of her talk is:

Recent Developments in Bridging the Semantic Gap Problem

Abstract: In this talk, I will present a summary of my PhD thesis which is about bridging the semantic gap between sensor data and ontological knowledge. The focus will be on the recent developments in heterogeneous knowledge integration as a solution for the semantic gap issue. I will also introduce the two research projects: Semantic Robot and E-care@home, with the goal of addressing the knowledge integration problem. In Semantic Robot, we are aiming to provide a semantic layer to a 3D topographic map and making the objects in the 3D map reasoning ready for different purposes such as querying and navigation. Likewise, in Ecare@home which is a Swedish interdisciplinary distributed research environment, our focus is on the development of methods that provide interpretation of the heterogeneous data coming from different types of sensors in conjunction with both medical and environmental knowledge in order to provide e-services for the elderly residing in their homes.

Time and date: 3.15pm, January 24, 2017

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


Semantic Web research at LiU

The Semantic Web is an extension of the traditional Web towards having machine processable content and interlinked data on the Web, with well-described semantics.

Ideally we would be able to view the whole Web as a large set of interconnected databases, which can be queried and browsed by software systems as well as human users. Semantic Web research at LiU includes areas such as ontologies and ontology engineering (ontology design patterns, ontology alignment and completion, ontology and alignment visualisation), graph databases and triple stores, querying the Web of data, RDF stream processing and complex event processing, as well as applications of these technologies in a number of fields, including open data, security, decision support systems, e-health and e-science, etc.

The aim of this blog is to report on the activities of our research group, and make results accessible to a wider audience.

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