Landia, N.; Anand, S. S.; Hotho, A.; Jäschke, R.; Doerfel, S. & Mitzlaff, F. (2012), Extending FolkRank with content data, in 'Proceedings of the 4th ACM RecSys workshop on Recommender systems and the social web' , ACM, New York, NY, USA , pp. 1--8 .
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Real-world tagging datasets have a large proportion of new/ untagged documents. Few approaches for recommending tags to a user for a document address this new item problem, concentrating instead on artificially created post-core datasets where it is guaranteed that the user as well as the document of each test post is known to the system and already has some tags assigned to it. In order to recommend tags for new documents, approaches are required which model documents not only based on the tags assigned to them in the past (if any), but also the content. In this paper we present a novel adaptation to the widely recognised FolkRank tag recommendation algorithm by including content data. We adapt the FolkRank graph to use word nodes instead of document nodes, enabling it to recommend tags for new documents based on their textual content. Our adaptations make FolkRank applicable to post-core 1 ie. the full real-world tagging datasets and address the new item problem in tag recommendation. For comparison, we also apply and evaluate the same methodology of including content on a simpler tag recommendation algorithm. This results in a less expensive recommender which suggests a combination of user related and document content related tags.</p> <p>Including content data into FolkRank shows an improvement over plain FolkRank on full tagging datasets. However, we also observe that our simpler content-aware tag recommender outperforms FolkRank with content data. Our results suggest that an optimisation of the weighting method of FolkRank is required to achieve better results.

Benz, D.; Hotho, A.; Jäschke, R.; Krause, B.; Mitzlaff, F.; Schmitz, C. & Stumme, G. (2010), 'The Social Bookmark and Publication Management System Bibsonomy', The VLDB Journal 19 (6) , 849--875 .
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Social resource sharing systems are central elements of the Web 2.0 and use the same kind of lightweight knowledge representation, called folksonomy. Their large user communities and ever-growing networks of user-generated content have made them an attractive object of investigation for researchers from different disciplines like Social Network Analysis, Data Mining, Information Retrieval or Knowledge Discovery. In this paper, we summarize and extend our work on different aspects of this branch of Web 2.0 research, demonstrated and evaluated within our own social bookmark and publication sharing system BibSonomy, which is currently among the three most popular systems of its kind. We structure this presentation along the different interaction phases of a user with our system, coupling the relevant research questions of each phase with the corresponding implementation issues. This approach reveals in a systematic fashion important aspects and results of the broad bandwidth of folksonomy research like capturing of emergent semantics, spam detection, ranking algorithms, analogies to search engine log data, personalized tag recommendations and information extraction techniques. We conclude that when integrating a real-life application like BibSonomy into research, certain constraints have to be considered; but in general, the tight interplay between our scientific work and the running system has made BibSonomy a valuable platform for demonstrating and evaluating Web 2.0 research.

2008

Glushko, R. J.; Maglio, P. P.; Matlock, T. & Barsalou, L. W. (2008), 'Categorization in the wild ', Trends in Cognitive Sciences 12 (4) , 129 - 135 .
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In studying categorization, cognitive science has focused primarily on cultural categorization, ignoring individual and institutional categorization. Because recent technological developments have made individual and institutional classification systems much more available and powerful, our understanding of the cognitive and social mechanisms that produce these systems is increasingly important. Furthermore, key aspects of categorization that have received little previous attention emerge from considering diverse types of categorization together, such as the social factors that create stability in classification systems, and the interoperability that shared conceptual systems establish between agents. Finally, the profound impact of recent technological developments on classification systems indicates that basic categorization mechanisms are highly adaptive, producing new classification systems as the situations in which they operate change.

Jäschke, R.; Hotho, A.; Schmitz, C.; Ganter, B. & Stumme, G. (2008), 'Discovering shared conceptualizations in folksonomies', Web Semant. 6 (1) , 38--53 .
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Social bookmarking tools are rapidly emerging on the Web. In such systems users are setting up lightweight conceptual structures called folksonomies. Unlike ontologies, shared conceptualizations are not formalized, but rather implicit. We present a new data mining task, the mining of all frequent tri-concepts, together with an efficient algorithm, for discovering these implicit shared conceptualizations. Our approach extends the data mining task of discovering all closed itemsets to three-dimensional data structures to allow for mining folksonomies. We provide a formal definition of the problem, and present an efficient algorithm for its solution. Finally, we show the applicability of our approach on three large real-world examples.

2008

Thom, R. J. Z. (H. N. Thom, N., ed. ( 2008 ), Moderne Personalentwicklung, Mitarbeiterpotenziale erkennen, entwickeln und fördern , Gabler .
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2007

Jäschke, R.; Hotho, A.; Schmitz, C. & Stumme, G. (2007), Analysis of the Publication Sharing Behaviour in BibSonomy, in U. Priss; S. Polovina & R. Hill, ed., 'Proceedings of the 15th International Conference on Conceptual Structures (ICCS 2007)' , Springer-Verlag, Berlin, Heidelberg , pp. 283--295 .
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BibSonomy is a web-based social resource sharing system which allows users to organise and share bookmarks and publications in a collaborative manner. In this paper we present the system, followed by a description of the insights in the structure of its bibliographic data that we gained by applying techniques we developed in the area of Formal Concept Analysis.

2006

Hoser, B.; Hotho, A.; J�schke, R.; Schmitz, C. & Stumme, G. (2006), Semantic Network Analysis of Ontologies, in 'European Semantic Web Conference, Budva, Montenegro' .
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A key argument for modeling knowledge in ontologies is the easy re-use and re-engineering of the knowledge. However, current ontology engineering tools provide only basic functionalities for analyzing ontologies. Since ontologies can be considered as 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 currently receive high attention in the Semantic Web community, there are only very few SNA applications, and virtually none for analyzing the structure of ontologies. We illustrate 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, we illustrate the insights these measures provide on two ontologies, which are different in purpose, scope, and size.

Hotho, A.; J�schke, R.; Schmitz, C. & Stumme, G. (2006), Emergent Semantics in BibSonomy, in Christian Hochberger & R�diger Liskowsky, ed., 'Informatik 2006 - Informatik f�r Menschen. Band 2' .
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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. 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, briefly describe our own system BibSonomy, which allows for sharing both bookmarks and publication references, and discuss first steps towards emergent semantics.

Hotho, A.; J?schke, R.; Schmitz, C. & Stumme, G. (2006), Information Retrieval in Folksonomies: Search and Ranking, in York Sure & John Domingue, ed., 'The Semantic Web: Research and Applications' , Springer, Heidelberg , pp. 411-426 .
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Hotho, A.; J�schke, R.; Schmitz, C. & Stumme, G. (2006), Information Retrieval in Folksonomies: Search and Ranking, in York Sure & John Domingue, ed., 'The Semantic Web: Research and Applications' , Springer, Heidelberg , pp. 411-426 .
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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. The reason for their immediate success is the fact that no specific skills are needed for participating. At the moment, however, 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.

Hotho, A.; Jäschke, R.; Schmitz, C. & Stumme, G. (2006), Trend detection in folksonomies, in 'Proceedings of the First international conference on Semantic and Digital Media Technologies' , Springer-Verlag, Berlin, Heidelberg , pp. 56--70 .
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As the number of resources on the web exceeds by far the number of documents one can track, it becomes increasingly difficult to remain up to date on ones own areas of interest. The problem becomes more severe with the increasing fraction of multimedia data, from which it is difficult to extract some conceptual description of their contents.</p> <p>One way to overcome this problem are social bookmark tools, which are rapidly emerging on the web. In such systems, users are setting up lightweight conceptual structures called folksonomies, and overcome thus the knowledge acquisition bottleneck. As more and more people participate in the effort, the use of a common vocabulary becomes more and more stable. We present an approach for discovering topic-specific trends within folksonomies. It is based on a differential adaptation of the PageRank algorithm to the triadic hypergraph structure of a folksonomy. The approach allows for any kind of data, as it does not rely on the internal structure of the documents. In particular, this allows to consider different data types in the same analysis step. We run experiments on a large-scale real-world snapshot of a social bookmarking system.

Schmitz, C.; Hotho, A.; J�schke, R. & Stumme, G. (2006), Kollaboratives Wissensmanagement , Springer , pp. 273-290 .
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Wissensmanagement in zentralisierten Wissensbasen erfordert einen hohen Aufwand f�r Erstellung und Wartung, und es entspricht nicht immer den Anforderungen der Benutzer. Wir geben in diesem Kapitel einen �berblick �ber zwei aktuelle Ans�tze, die durch kollaboratives Wissensmanagement diese Probleme l�sen k�nnen. Im Peer-to-Peer-Wissensmanagement unterhalten Benutzer dezentrale Wissensbasen, die dann vernetzt werden k�nnen, um andere Benutzer eigene Inhalte nutzen zu lassen. Folksonomies versprechen, die Wissensakquisition so einfach wie m�glich zu gestalten und so viele Benutzer in den Aufbau und die Pflege einer gemeinsamen Wissensbasis einzubeziehen.

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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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.