The intent of this element is to provide a means to express relationships among resources that have formal relationships to others, but exist as discrete resources themselves. For example, images in a document, chapters in a book, or items in a collection. Users and developers should understand that use of this element is currently considered to be experimental. URN Uniform Resource Name for the resource. ISBN Internatonal Standard Book Number for the resource.
Different types are under development.
Concerning the DC Qualifier TYPE it is most likely that we can see developments within the context of collection-level descriptions. Subelements may be defined at a later date.