provides attributes which can be used to associate a representation such as a name or title with canonical information about the object being named or referenced. provides an externally-defined means of identifying the entity (or entities) being named, using a coded value of some kind. any string of Unicode characters

The value may be a unique identifier from a database, or any other externally-defined string identifying the referent.

reference provides an explicit means of locating a full definition for the entity being named by means of one or more URIs.

The value must point directly to one or more XML elements by means of one or more URIs, separated by whitespace. If more than one is supplied, the implication is that the name identifies several distinct entities.