These aim for specifying tagging data in a formal way. The data formats for common conceptualization of tagging data can be represented by an ontology to make a minimal commitment.
Methods and APIs
aims to collect, share, or exchange tagging data, or create a bridge among heterogeneous social tagging sites, methods should implement by types of mashups
supports a social ecosystem that interlinks among diverse objects such as individual and individual, individual and communities, or individual and the tags themselves and leverages social connections based on tags.