TaggedItem
From TagCommons
A TaggedItem is a thing that is tagged. At the level of conceptualization, we don't need to restrict this other than to say it is something that can be identified universally. That is, it must be something that has a persistent identity that can be used outside of the context of the specific application or tag data source. Since the purpose of this tag ontology is the interoperability of tags across domains, the context-independence of the identity is the essential property.
For all applications in our use cases, a TaggedItem could be identified by a [URN]. For example, if one were to tag a book with "fiction", the book might be identified by its ISBN identifer using a URN such as urn:isbn:0895773228.
Why a URN and URL? Not all use cases require a URL, although translating into some formats such as [Microformat's rel-tag] will require a working URL . This is a pragmatic, rather than semantic, requirement. It is also important to remember that the semantics of the TaggedItem is not the URN itself, but the thing named by the URN. In other words, taggings are not assertions about strings (URNs), they are assertions about entities such as books. Other semantic web agents might reason about the identity of tagged things using the URN, mapping it to various URLs or other URNs. For example, even ISBN is not a unique identifier of books, since it does not account for editions. So an agent that wants to find all the tags for a book might reason about the various names for the book and gather the tag data from multiple sources, each which have different ways of referring to books.
