Information Systems Group

― Knowledge Representation and Reasoning

Giorgos Stoilos

Research Assistant


My research interests include most aspects of knowledge representation and automated reasoning, especially focused on Description Logics (DLs) and ontology languages, such as OWL, as well as their application in areas like the Semantic Web and Multimedia. Recently I work on the topic of automatic evaluation and benchmarking of Description Logic and Semantic Web query answering systems, where I have designed and developed methods for the automatic generation of synthetic testing data and conjunctive queries. Most algorithms have been implemented in the prototype SyGENiA tool. Furthermore, I participate in the development of the HermiT reasoner where I have developed HermiT's new optimised classification algorithm. I am also currently working on query rewriting algorithms and semantic approximation.

In the past, I have also worked on the problem of representing and reasoning with fuzzy knowledge where I have developed fuzzy extensions of Description Logics and OWL, as well as a number of tableaux reasoning algorithms for them. Several of the algorithms have been implemented in the FiRE fuzzy reasoner and the ONTOSEARCH2 system. Last but not least I have also worked in the area of knowledge interoperability and ontology alignment, where I designed a new String similarity method, called Iterative-SubString (I-Sub), which has been integrated in several popular Ontology Alignment and Schema Matching Systems and recently in the NLP package of SWI-prolog.


Before coming to Oxford, I worked as a Research Assistant in the Image, Video and Multimedia Laboratory, Electrical and Computer Engineering, National and Technical University of Athens, where I also obtained my PhD under the joint supervision of Prof. Stefanos Kollias and Lecturer Giorgos Stamou. During my stay there I had the opportunity to work in a number of EU funded research projects, like the IP project X-Media, STREP project BOEMIE for which I also acted as a WP leader and NoE projects Knowledge Web and K-Space.


Outstanding paper award at the 24th AAAI Conference on Artificial Intelligence, for the paper "How Incomplete Is Your Semantic Web Reasoner?".

Best Thesis award in the National and Technical University of Athens, sponsored by the Chorafas Institute.

Recent Publications

Optimising Ontology Classification by Birte Glimm, Ian Horrocks, Boris Motik and Giorgos Stoilos. In Proceedings of the Ninth International Semantic Web Conference (ISWC 2010).

What to Ask to An Incomplete Semantic Web Reasoner? by Bernardo Cuenca Grau and Giorgos Stoilos. In Proceedings of the 22nd International Joint Conference on Artificial Intelligence (IJCAI−2011).

How Incomplete is your Semantic Web Reasoner? by Giorgos Stoilos, Bernardo Cuenca Grau and Ian Horrocks. In Proceedings of the Twenty-Fourth AAAI Conference on Artificial Intelligence (AAAI 2010). AAAI Press. 2010.


In my younger days I used to play tennis at a sub-professional level in the Juniors categories. I used to be a member of the Greek national team under the 18 and played in many European championships, where I had the opportunity to meet and play with people that are now competing in Grand Slams. In 1998 we managed to come 8th at the European Team Championship 18U/Edmond de Galea Cup. Whenever I find extra time from research I also go and play with Oxford's blues team.


Giorgos Stoilos


Research Assistant



Contact Information

Room 307, Wolfson Building, Parks Road
Oxford OX1 3QD


IQAROS Query Rewriting System

HermiT reasoner



3 papers accepted in IJCAI'17

Three papers co-authored by the KRR group have been accepted in IJCAI'17:
- "Query Reformulation: Theory and Practice" by M. Benedikt, E. V. Kostylev, F. Mogavero, and E. Tsamoura;
- "Foundations of Declarative Data Analysis Using Limit Datalog Programs" by M. Kaminski, B. Cuenca Grau, B. Motik, E. V. Kostylev, and I. Horrocks; and
- "The Bag Semantics of Ontology-Based Data Access" by C. Nikolaou, E. V. Kostylev, G. Konstantinidis, M. Kaminski, B. Cuenca Grau, and I. Horrocks.

Paper accepted in PODS'17

The paper entitled "Benchmarking the chase" authored by Michael Benedikt, George Konstantinidis, Giansalvatore Mecca, Boris Motik, Paolo Papotti, Donatello Santoro, and Efthymia Tsamoura has been accepted in PODS'17.

Andrew Bate defends his PhD Thesis

Andrew Bate has successfully defended his PhD Thesis on Consequence Based Reasoning. Congratulations to Dr. Andrew Bate!

Best applications paper award at ISWC'16

Our paper entitled "Semantic Technologies for Data Analysis in Health Care" received the Best Applications Paper Award at the International Semantic Web Conference (ISWC 2016).

4 papers accepted in ISWC'16

Four papers authored by the KRR group have been accepted in the International Semantic Web Conference (ISWC 2016).

Best paper award at ICDT'16

Mark Kaminski and Egor Kostylev received the best paper award at ICDT 2016 for their paper entitled "Beyond Well-Designed SPARQL".