Collaborative tagging websites or systems allow users to associate freely-determined keywords (tags) with a particular resource. The collection of users’ tags and resources is referred to as a folksonomy. Unlike traditional forms of metadata, the meaning of, and relationships between, tags are not rigorously defined, limiting the usefulness of tag-based metadata.

We propose a novel approach to enrich tagging systems by constructing a tag ontology that captures semantic relationships among tags. We first consider regularities that can be exploited in a folksonomy. Then, we show how user-level tag vocabulary can be used for tag meaning disambiguation. Following this, we introduce a distance model to calculate the relatedness of two sets of resources within a folksonomy, and use this to develop a method for discovering tag relations.