Item and Record
It is important to make a distinction between Item and Record. The protocol text states:
"...An item is conceptually a container that stores or dynamically generates metadata about a single resource in multiple formats, each of which can be harvested as records via the OAI-PMH. [...] A record is metadata expressed in a single format. A record is returned in an XML-encoded byte stream in response to an OAI-PMH request for metadata from an item..."[bold added by MF]
Within DRIVER it is recommend to construct the XML-encoded stream according to the XML- Container specifications. These specifications are given below.
The Unique Identifier identifies an item within a repository. Do not confuse this identifier with the element dc:identifier in Dublin Core. The OAI identifier has a different function: it is used to extract metadata, whereas the DC identifier is used to extract the resource. Schematically: