The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Methods and Applications for Ontology-Based Recommender Systems

Tuukka Ruotsalo

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium AS1 at the Aalto University School of Science and Technology (Espoo, Finland) on the 7th of June 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3151-4)   [1711 KB]
Dissertation is also available in print (ISBN 978-952-60-3150-7)


Recommender systems are a specific type of information filtering systems used to identify a set of objects that are relevant to a user. Instead of a user actively searching for information, recommender systems provide advice to users about objects they might wish to examine. Content-based recommender systems deal with problems related to analyzing the content, making heterogeneous content interoperable, and retrieving relevant content for the user.

This thesis explores ontology-based methods to reduce these problems and to evaluate the applicability of the methods in recommender systems. First, the content analysis is improved by developing an automatic annotation method that produces structured ontology-based annotations from text. Second, an event-based method is developed to enable interoperability of heterogeneous content representations. Third, methods for semantic content retrieval are developed to determine relevant objects for the user.

The methods are implemented as part of recommender systems in two cultural heritage information systems: CULTURESAMPO and SMARTMUSEUM. The performance of the methods were evaluated through user studies. The results can be divided into five parts. First, the results show improvement in automatic content analysis compared to state of the art methods and achieve performance close to human annotators. Second, the results show that the event-based method developed is suitable for bridging heterogeneous content representations. Third, the retrieval methods show accurate performance compared to user opinions. Fourth, semantic distance measures are compared to study the best query expansion strategy. Finally, practical solutions are developed to enable user profiling and result clustering.

The results show that ontology-based methods enable interoperability of heterogeneous knowledge representations and result in accurate recommendations. The deployment of the methods to practical recommender systems show applicability of the results in real life settings.

This thesis consists of an overview and of the following 5 publications:

  1. Tuukka Ruotsalo and Eero Hyvönen. 2007. An event-based approach for semantic metadata interoperability. In: Karl Aberer, Key-Sun Choi, Natasha Noy, Dean Allemang, Kyung-Il Lee, Lyndon Nixon, Jennifer Golbeck, Peter Mika, Diana Maynard, Riichiro Mizoguchi, Guus Schreiber, and Philippe Cudré-Mauroux (editors). The Semantic Web. Proceedings of the 6th International Semantic Web Conference and the 2nd Asian Semantic Web Conference (ISWC 2007 + ASWC 2007). Busan, Korea. 11-15 November 2007. Berlin, Heidelberg, Germany. Springer. Lecture Notes in Computer Science, volume 4825, pages 409-422. ISBN 978-3-540-76297-3.
  2. Tuukka Ruotsalo and Eero Hyvönen. 2007. A method for determining ontology-based semantic relevance. In: Roland Wagner, Norman Revell, and Günther Pernul (editors). Proceedings of the 18th International Conference on Database and Expert Systems Applications (DEXA 2007). Regensburg, Germany. 3-7 September 2007. Berlin, Heidelberg, Germany. Springer. Lecture Notes in Computer Science, volume 4653, pages 680-688. ISBN 978-3-540-74467-2.
  3. Tuukka Ruotsalo, Lora Aroyo, and Guus Schreiber. 2009. Knowledge-based linguistic annotation of digital cultural heritage collections. IEEE Intelligent Systems, volume 24, number 2, pages 64-75.
  4. Tuukka Ruotsalo, Eetu Mäkelä, Tomi Kauppinen, Eero Hyvönen, Krister Haav, Ville Rantala, Matias Frosterus, Nima Dokoohaki, and Mihhail Matskin. 2009. Smartmuseum: Personalized context-aware access to digital cultural heritage. In: Proceedings of the International Conference on Digital Libraries and the Semantic Web 2009 (ICSD 2009). Università di Trento, Trento, Italy. 8-11 September 2009, pages 178-192.
  5. Tuukka Ruotsalo and Eetu Mäkelä. 2009. A comparison of corpus-based and structural methods on approximation of semantic relatedness in ontologies. International Journal on Semantic Web and Information Systems, volume 5, number 4, pages 39-56.

Errata of publications 2 and 4

Keywords: ontology-based recommender systems, information storage, information retrieval, content analysis

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2010 Aalto University School of Science and Technology

Last update 2011-05-26