Scheme

The Scheme attribute, if present, serves to distinguish which of possibly multiple naming schemes in the controlled vocabulary is the one that governs this FormalName. For a match to be obtained within the controlled vocabulary, the rule is that the FormalName and the Scheme must both match. If there is a Scheme attribute on the current element, then both the FormalName and the Scheme in the controlled vocabulary must match. The controlled vocabulary will be located either through the Vocabulary attribute (if present) or through the appropriate Catalog entry where the Context matches the current element. If a Vocabulary attribute is present that points to a TopicSet then the FormalName may be resolved using this TopicSet. This overrides any relevant Catalog entry.  If there is no Scheme attribute on the current element and no Vocabulary attribute then a Scheme may be assigned through as follows: If the Catalog, within the instance or externally referenced from the instance, contains a Resource element with a DefaultVocabularyFor child element with a Context attribute that matches the current element and a Scheme attribute with a value declared, then this Scheme may be applied when resolving the current element FormalName. If the DefaultVocabularyFor has no Scheme value then a match will be to an item in the vocabulary that has the current FormalName and no Scheme.