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Top1. Introduction
In this day of read-write Web, users emerged from passive content consumers to producers of various kinds of Web content. Most visible among these kinds is user-generated primary content that has become an everyday source of information and knowledge. Yahoo! Answers and Wikipedia are two prime examples of such primary user-generated content, and they present two different but successful models of community authoring. Less visible, but equally important is user-generated secondary content, produced by the users in association with different kinds of traditional and social primary content. Amazon.com product ratings and reviews, blog post comments, Delicious notes and tags are examples of highly popular secondary content.
E-Learning landscape has been equally affected by the gradual transition of users from consumers to producers. However, the balance between primary and secondary content in E-Learning is different. Instructors and other users with good domain knowledge nowadays mostly generate primary content in E-Learning. A good example is provided by communities of practice that now routinely generate learning resources through community authoring. In contrast, secondary content is typically generated by students who are rarely capable to generate primary content. Student annotations on lecture slides or electronic texts (henceforth, we refer to this as course notes), discussions of the topics introduced by instructors, ratings of learning content and even student paths through learning content are examples of student-generated and other primary content creators, the majority of modern research on social E-Learning systems focus on student-generated content. The main idea behind these research efforts is that by enabling students to access various kinds of content generated by other students we can significantly improve both the quality of learning and student motivation to learn. For example, the ability to see comments provided by other students to an assigned textbook chapter might help in better understanding its content and relating it to the assigned homework (Farzan & Brusilovsky, 2008). The ability to see the progress of other students working on educational exercises might provide additional motivation to learn (Hsiao, Bakalov, Brusilovksy, & Konig-Ries, 2011).
A range of tools has been created to implement the ideas of social learning, i.e., to assist students in organizing, sharing, and accessing this social content. Among these tools most popular nowadays are social E-Learning portals (Dicheva & Dichev, 2010; Abel, Marenzi, Nejdl, & Zerr, 2009; Wolpers, Memmel, & Giretti, 2009; Janssen et al., 2007). A typical social E-Learning portal simply provides access to a range of primary learning content and enables the students to produce and share various kinds of primary and secondary content: presentation, notes, discussions, bookmarks, comments, ratings, tags, etc. Frequently, these portals also allow end users to produce an easy integration of external social content such as YouTube videos, Delicious bookmarks, or Flickr images.