There are two main approaches to subject classification currently being explored for future use in DITA, which this page will call the map-based approach and the metadata approach.

In the map-based approach, a taxonomy is represented using a hierarchy in a DITA map. Each member of the hierarchy is a specialization of the <topicref> element. Each <topicref> element points to a topic that describes the subject of that node of the taxonomy.

In the metadata approach, the <data> element (which is being introduced in DITA 1.1) is used to record properties. The property stated in a <data> element is considered to apply to:

• the enclosing element (the default)
• another element (if a URI is specified)
• an external object (if a sub-element is used and a URI is specified in the sub-element)

When the <data> element is used within content, the property that it states is considered to apply to the directly enclosing content element. When the <data> element is used in metadata contexts, the property that it states is considered to apply to the nearest enclosing content element (such as <topic>).

Broader topics:

• Taxonomies and subject classification
• Enhancements

Related topic: Taxonomy specialization plug-in, Introduction to Specialization