The data management system within which an identifier is in scope and therefore unique. This is typically a URL (Uniform Resource Locator) that indicates a data management system. All identifiers that share a system must be unique. In other words, if the same identifier is used in two locations with identical systems, then by definition the objects at which they point are in fact the same object. Example(s): http://metacat.somewhere.org/svc/mc/
An additional, secondary identifier for this entity. The primary identifier belongs in the reference table, but additional identifiers that are used to label this entity, possibly from different data management systems, can be listed here. Example: VCR3465