Tagging Web 2.0 content in context

Tags have been investigated for users' behaviour and for tags' semantics. However, yet lacking is an investigation of tag's usability from the design perspective, specifically for their coherence and stability as part of online community sites. While the unstructured approach to tagging is a contribution to tags' popularity, there is also in this to set a usability hurdle, i.e., in the context of exploratory search and web-based learning. Against this background, this article suggests an ontology of eight elements for guiding context-aware tagging, namely, SKeTCo. The eight elements represent a three-perspective view of core categories required for effective tagging. We illustrate the feasibility and usefulness of the suggested approach based on empirical investigation conducted with graduate and undergraduate students in two different institutions and discuss its usability against usability factors adopted from the literature. This work should prove specifically useful for Web 2.0 users and for designers involved in learning and in exploratory search.