Social resource sharing systems like YouTube and del.icio.us have acquired a large number of users within the last few years. They provide rich resources for data analysis, information retrieval, and knowledge discovery applications. A first step towards this end is to gain better insights into
content and structure of these systems. In this paper, we will analyse the main network characteristics of two of the
systems. We consider their underlying data structures – socalled folksonomies – as tri-partite hypergraphs, and adapt
classical network measures like characteristic path length and clustering coefficient to them.
Subsequently, we introduce a network of tag co-occurrence and investigate some of its statistical properties, focusing on
correlations in node connectivity and pointing out features
that reflect emergent semantics within the folksonomy. We show that simple statistical indicators unambiguously spot non-social behavior such as spam.