The MADCOWannotation system supports a notion of group, facilitating focused annotations with respect to a
domain. In previous work, we adopted ontologies to represent knowledge
about domains, allowing more refined annotations to a group, and
discussed how the use of ontologies facilitates the formulation of
semantically significant queries for retrieving annotations on specific
topics. We now expand on previous results and study two new types of
measures to identify matches between users’ interests and groups: Degree
Centrality, developed for social networks to assess the quality of
concepts in an ontology, and URL concordance, indicating the similarity
of interests among users who annotate the same pages.