From harmoni

The Harmoni Taggging service provides a system for recording and retrieving of Tags mapped to item Ids. A Tag is a string classifier. Tags are associated with the Id of the item being tagged and the agent id of the person who created the tag. All tags created by an agent can be retrieved, or all tags applied to an item id, or all tags in the system.

Extensible TaggedItem classes provide a mapping between an item id and more information about the thing being tagged. The HarmoniNodeTaggedItem provides the display name, description, url, and thumbnail url to a Hierarchy Node or Repository Asset. The UrlTaggedItem allows for tags on arbitrary URLs. more to come...