Social Tagging Recommender Systems

The new generation of Web applications known as (STS) is successfully established and poised for continued growth. STS are open and inherently social; features that have been proven to encourage participation. But while STS bring new opportunities, they revive old problems, such as information overload. Recommender Systems are well known applications for increasing the level of relevant content over the “noise” that continuously grows as more and more content becomes available online. In STS however, we face new challenges. Users are interested in finding not only content, but also tags and even other users. Moreover, while traditional recommender systems usually operate over 2-way data arrays, STS data is represented as a third-order tensor or a hypergraph with hyperedges denoting (user, resource, tag) triples. In this chapter, we survey the most recent and state-of-the-art work about a whole new generation of recommender systems built to serve STS. We describe (a) novel facets of recommenders for STS, such as user, resource, and tag recommenders, (b) new approaches and algorithms for dealing with the ternary nature of STS data, and (c) recommender systems deployed in real world STS. Moreover, a concise comparison between existing works is presented, through which we identify and point out new research directions. Leandro Balby Marinho · Alexandros Nanopoulos · Lars Schmidt-Thieme Information Systems and Machine Learning Lab (ISMLL), University of Hildesheim, Marienburger Platz 22, 31141 Hildesheim, Germany, http://www.ismll.uni-hildesheim.de, e-mail: {marinho,nanopoulos,schmidt-thieme}@ismll.uni-hildesheim.de Robert Jäschke · Andreas Hotho · Gerd Stumme Knowledge & Data Engineering Group (KDE), University of Kassel, Wilhelmshöher Allee 73, 34121 Kassel, Germany, http://www.kde.cs.uni-kassel.de, e-mail: {jaeschke,hotho,stumme}@cs. uni-kassel.de Panagiotis Symeonidis Department of Informatics, Aristotle University, 54124 Thessaloniki, Greece, e-mail: symeon@ csd.auth.gr F. Ricci et al. (eds.), Recommender Systems Handbook, DOI 10.1007/978-0-387-85820-3_19, © Springer Science+Business Media, LLC 2011 615 616 Leandro Balby Marinho et al.