Change Log: 6/05/2007 (J. Pantella) -- Created pursuant to approved CR 2007-1. See also http://metadata.dod.mil/irs/DDMS/cm/CR/2007/DDMS_CR_2007-1. 1/3/2007 (J. Pantella) -- Modified version attribute to reflect that this is version 1.4.2. 7/1/2008 (D. Barclay) -- Made elements "extent" and "medium" optional in type MediaType (per DDMS-CR-2008-6). 7/15/2008 (J. Pantella) -- Modified security attributes on creator, publisher, and contributor to be optional, added optional security attributes to pointOfContact for consistency across the elements. 7/15/2008 (J. Pantella) -- Modified version to reflect that this is version 2.0. 1/5/2010 (P. Lunceford) -- Created DDMS 3.0. Implemented CRs 2009-04 (replaced creatorType/publisherType/contributorType/pointOfContactType with contactInfoType), 2009-07 (set minOccurs on RelatedResourceType to 1), 2009-09 (added Unknown entity to accompany Person, Organization, and Service for a choice for Creator, Publisher, Contributor, and PointOfContact), 2009-10 (added extensions to CompoundKeywordIdentifierType and CompoundCategoryIdentifierType), and 2009-12 (added Security Markings to SubjectCoverageType, CompoundSouceIdentifierType, TemporalCoverageType, and VirtualCoverageType).