Jäschke, R.; Marinho, L. B.; Hotho, A.; Schmidt-Thieme, L. & Stumme, G. (2007), Tag Recommendations in Folksonomies, in Joost N. Kok; Jacek Koronacki; Ramon López de Mántaras; Stan Matwin; Dunja Mladenic & Andrzej Skowron, ed., 'Knowledge Discovery in Databases: PKDD 2007, 11th European Conference on Principles and Practice of Knowledge Discovery in Databases' , Springer, Berlin, Heidelberg , pp. 506-514 .
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Collaborative tagging systems allow users to assign keywords—so called “tags”—to resources. Tags are used for navigation, finding resources and serendipitous browsing and thus provide an immediate benefit for users. These systems usually include tag recommendation mechanisms easing the process of finding good tags for a resource, but also consolidating the tag vocabulary across users. In practice, however, only very basic recommendation strategies are applied. In this paper we evaluate and compare two recommendation algorithms on largescale real life datasets: an adaptation of user-based collaborative filtering and a graph-based recommender built on top of FolkRank. We show that both provide better results than non-personalized baseline methods. Especially the graph-based recommender outperforms existing methods considerably.

Alani, H.; Hoser, B.; Schmitz, C. & Stumme, G., ed. (2006), Proceedings of the 2nd Workshop on Semantic Network Analysis .
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Hoser, B.; Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), Semantic Network Analysis of Ontologies, in York Sure & John Domingue, ed., 'The Semantic Web: Research and Applications' , Springer, Heidelberg , pp. 514-529 .
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A key argument for modeling knowledge in ontologies is the easy re-use and re-engineering of the knowledge. However, beside consistency checking, current ontology engineering tools provide only basic functionalities for analyzing ontologies. Since ontologies can be considered as (labeled, directed) graphs, graph analysis techniques are a suitable answer for this need. Graph analysis has been performed by sociologists for over 60 years, and resulted in the vivid research area of Social Network Analysis (SNA). While social network structures in general currently receive high attention in the Semantic Web community, there are only very few SNA applications up to now, and virtually none for analyzing the structure of ontologies. We illustrate in this paper the benefits of applying SNA to ontologies and the Semantic Web, and discuss which research topics arise on the edge between the two areas. In particular, we discuss how different notions of centrality describe the core content and structure of an ontology. From the rather simple notion of degree centrality over betweenness centrality to the more complex eigenvector centrality based on Hermitian matrices, we illustrate the insights these measures provide on two ontologies, which are different in purpose, scope, and size.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), BibSonomy: A Social Bookmark and Publication Sharing System, in Aldo de Moor; Simon Polovina & Harry Delugach, ed., 'Proceedings of the First Conceptual Structures Tool Interoperability Workshop at the 14th International Conference on Conceptual Structures' , Aalborg Universitetsforlag, Aalborg , pp. 87-102 .
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Social bookmark tools are rapidly emerging on the Web. In suchsystems users are setting up lightweight conceptual structurescalled folksonomies. The reason for their immediate success is thefact that no specific skills are needed for participating. In thispaper we specify a formal model for folksonomies and briefly describe our own system BibSonomy, which allows for sharing both bookmarksand publication references in a kind of personal library.

Social bookmark tools are rapidly emerging on the Web. In such systems users are setting up lightweight conceptual structures called folksonomies. The reason for their immediate success is the fact that no specific skills are needed for participating. In this paper we specify a formal model for folksonomies and briefly describe our own system BibSonomy, which allows for sharing both bookmarks and publication references in a kind of personal library.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), Das Entstehen von Semantik in BibSonomy, in 'Social Software in der Wertschöpfung' , Nomos, Baden-Baden .
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Immer mehr Soziale-Lesezeichen-Systeme entstehen im heutigen Web. In solchen Systemen erstellen die Nutzer leichtgewichtige begriffliche Strukturen, so genannte Folksonomies. Ihren Erfolg verdanken sie der Tatsache, dass man keine speziellen Fähigkeiten benötigt, um an der Gestaltung mitzuwirken. In diesem Artikel beschreiben wir unser System BibSonomy. Es erlaubt das Speichern, Verwalten und Austauschen sowohl von Lesezeichen (Bookmarks) als auch von Literaturreferenzen in Form von BibTeX-Einträgen. Die Entwicklung des verwendeten Vokabulars und der damit einhergehenden Entstehung einer gemeinsamen Semantik wird detailliert diskutiert.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), Emergent Semantics in BibSonomy, in Christian Hochberger & Rüdiger Liskowsky, ed., 'Informatik 2006 -- Informatik für Menschen. Band 2' , Gesellschaft für Informatik, Bonn .
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Social bookmark tools are rapidly emerging on the Web. In suchsystems users are setting up lightweight conceptual structurescalled folksonomies. The reason for their immediate success is thefact that no specific skills are needed for participating. In thispaper we specify a formal model for folksonomies, briefly describeour own system BibSonomy, which allows for sharing both bookmarks andpublication references, and discuss first steps towards emergent semantics.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), FolkRank: A Ranking Algorithm for Folksonomies, in 'Proc. FGIR 2006' .
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In social bookmark tools users are setting up lightweight conceptual structures called folksonomies. Currently, the information retrieval support is limited. We present a formal model and a new search algorithm for folksonomies, called FolkRank, that exploits the structure of the folksonomy. The proposed algorithm is also applied to find communities within the folksonomy and is used to structure search results. All findings are demonstrated on a large scale dataset. A long version of this paper has been published at the European Semantic Web Conference 2006.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), Trend Detection in Folksonomies, in Yannis S. Avrithis; Yiannis Kompatsiaris; Steffen Staab & Noel E. O'Connor, ed., 'Proc. First International Conference on Semantics And Digital Media Technology (SAMT) ' , Springer, Heidelberg , pp. 56-70 .
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As the number of resources on the web exceeds by far the number ofdocuments one can track, it becomes increasingly difficult to remainup to date on ones own areas of interest. The problem becomes moresevere with the increasing fraction of multimedia data, from whichit is difficult to extract some conceptual description of theircontents.One way to overcome this problem are social bookmark tools, whichare rapidly emerging on the web. In such systems, users are settingup lightweight conceptual structures called folksonomies, andovercome thus the knowledge acquisition bottleneck. As more and morepeople participate in the effort, the use of a common vocabularybecomes more and more stable. We present an approach for discoveringtopic-specific trends within folksonomies. It is based on adifferential adaptation of the PageRank algorithm to the triadichypergraph structure of a folksonomy. The approach allows for anykind of data, as it does not rely on the internal structure of thedocuments. In particular, this allows to consider different datatypes in the same analysis step. We run experiments on a large-scalereal-world snapshot of a social bookmarking system.

Jäschke, R.; Hotho, A.; Schmitz, C.; Ganter, B. & Stumme, G. (2006), TRIAS - An Algorithm for Mining Iceberg Tri-Lattices, in 'Proceedings of the 6th IEEE International Conference on Data Mining (ICDM 06)' , IEEE Computer Society, Hong Kong , pp. 907-911 .
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Jäschke, R.; Hotho, A.; Schmitz, C. & Stumme, G. (2006), Wege zur Entdeckung von Communities in Folksonomies, in Stefan Braß & Alexander Hinneburg, ed., 'Proc. 18. Workshop Grundlagen von Datenbanken' , Martin-Luther-Universität , Halle-Wittenberg , pp. 80-84 .
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Ein wichtiger Baustein des neu entdeckten World Wide Web -- des "`Web 2.0"' -- stellen Folksonomies dar. In diesen Systemen können Benutzer gemeinsam Ressourcen verwalten und mit Schlagwörtern versehen. Die dadurch entstehenden begrifflichen Strukturen stellen ein interessantes Forschungsfeld dar. Dieser Artikel untersucht Ansätze und Wege zur Entdeckung und Strukturierung von Nutzergruppen ("Communities") in Folksonomies.

Schmitz, C.; Hotho, A.; Jäschke, R. & Stumme, G. (2006), Content Aggregation on Knowledge Bases using Graph Clustering, in York Sure & John Domingue, ed., 'The Semantic Web: Research and Applications' , Springer, Heidelberg , pp. 530-544 .
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Recently, research projects such as PADLR and SWAP have developed tools like Edutella or Bibster, which are targeted at establishing peer-to-peer knowledge management (P2PKM) systems. In such a system, it is necessary to obtain provide brief semantic descriptions of peers, so that routing algorithms or matchmaking processes can make decisions about which communities peers should belong to, or to which peers a given query should be forwarded. This paper provides a graph clustering technique on knowledge bases for that purpose. Using this clustering, we can show that our strategy requires up to 58% fewer queries than the baselines to yield full recall in a bibliographic P2PKM scenario.

Schmitz, C.; Hotho, A.; Jäschke, R. & Stumme, G. (2006), Mining Association Rules in Folksonomies, in V. Batagelj; H.-H. Bock; A. Ferligoj & A. �iberna, ed., 'Data Science and Classification. Proceedings of the 10th IFCS Conf.' , Springer, Heidelberg , pp. 261--270 .
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Social bookmark tools are rapidly emerging on the Web. In such systems users are setting up lightweight conceptual structures called folksonomies. These systems provide currently relatively few structure. We discuss in this paper, how association rule mining can be adopted to analyze and structure folksonomies, and how the results can be used for ontology learning and supporting emergent semantics. We demonstrate our approach on a large scale dataset stemming from an online system.

Schmitz, C.; Hotho, A.; J�schke, R. & Stumme, G. (2006), Mining Association Rules in Folksonomies, in V. Batagelj; H.-H. Bock; A. Ferligoj & A. �iberna, ed., 'Data Science and Classification. Proceedings of the 10th IFCS Conf.' , Springer, Heidelberg , pp. 261--270 .
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Schmitz, C.; Hotho, A.; Jäschke, R. & Stumme, G. (2006), Mining Association Rules in Folksonomies, in V. Batagelj; H.-H. Bock; A. Ferligoj & A. Žiberna, ed., 'Data Science and Classification. Proceedings of the 10th IFCS Conf.' , Springer, Heidelberg , pp. 261--270 .
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2005

Stumme, G.; Hoser, B.; Schmitz, C. & Alani, H., ed. (2005), Proceedings of the First Workshop on Semantic Network Analysis , CEUR Proceedings , Aachen .
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2003

Cole, R. J.; Eklund, P. W. & Stumme, G. (2003), 'Document Retrieval for Email Search and Discovery using Formal Concept Analysis', Journal of Applied Artificial Intelligence (AAI) 17 (3) , 257-280 .
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This paper discusses an document discovery tool based on conceptual clustering by formal concept analysis. The program allows users to navigate email using a visual lattice metaphor rather than a tree. It implements a virtual file structure over email where files and entire directories can appear in multiple positions. The content and shape of the lattice formed by the conceptual ontology can assist in email discovery. The system described provides more flexibility in retrieving stored emails than what is normally available in email clients. The paper discusses how conceptual ontologies can leverage traditional document retrieval systems and aid knowledge discovery in document collections.