This work is licensed under the Creative Commons Attribution-ShareAlike License. To view a copy of this license, see the file license.txt, visit http://creativecommons.org/licenses/by-sa/1.0 or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. This component schema provides attribute group declarations for metadata elements to support strict validation of element uniqueness constraints, by providing the attribute uniqueElementName for each metadata element that should appear with multiplicity at most one.