A subject scheme map is used to define sets of controlled values for use in classifying content. Sets of controlled values can be bound to DITA attributes. This allows DITA users to share the controlled values for an information set without having to modify a DTD or XML schema. The list of available values can be modified quickly to adapt to new situations, without the need to manage updates to a document type. In addition, DITA users can define relationships between controlled values and extend a set of controlled values maintained by another team or organization. The list of defined values are not validated by basic XML parsers. Instead, the defined values should be validated by DITA processors.
The remaining elements in the subject scheme map are used to make more precise statements about how values in a taxonomy relate to one another.