Social Tagging: Semantics are Actually Used

This paper describes the results of a study whose goal is to analyze, evaluate and understand the use of semantics in social networks. As a paradigmatic example, the study concentrates on a fairly large portion of the tags used in del.icio.us (more than 5,000 tags). The results show that semantics are pervasively used. In particular, the large majority (in our experiment, 75%) of the tags are subject related and directly codify the semantics of the resource. Furthermore, the number of tags which are effectively used is only a small proportion of the overall tag set (in our experiment around 30% of the tags covers around 95% of the resources), and these tags tend to remain stable in time, despite the continuous growth of the number of tags and resources being indexed. Finally, it is possible to identify an implicit use of hierarchical relationships (i.e., lightweight ontologies) among the concepts denoted by the terms used.