ded:Definition: An element under the subjectCoverage element which is a natural
language indication of the resource's subject matter. A natural language
indication of the resource's subject matter. See IRM Spec Category:
Subject.
ded:Obligation: (Conditional) At least one of category or keyword.
ded:Comment: The number of keyword elements that can be included in the
subjectCoverage is unbounded. When there are more than one category element the
additional category entries must occur before any keyword elements.