Instances of Availability
Individual Resource entity: metadata which is general and non-specific to any instance of a resource.
Resource Instance entity: metadata about a particular instance of a resource.
A particular journal title may be available:
- in full-text (last five years), via a web based service
- as abstracts only (last ten years), on a cd-rom
- in hard copy (last twelve years), in the library
depth + date range + medium