An identifier of some specialization within the reference type. For example, technical reports are labeled with types-of-work such as ``technical report'' and ``memo''. Dissertations are specialized by the level of the associated degree.
(=> (Ref.Type-Of-Work ?Ref ?Name)
(Or (Thesis-Reference ?Ref)
(Technical-Report-Reference ?Ref)
(Misc-Publication-Reference ?Ref)))