Specialization is the process of creating new categories of topics, or information types, as well as new categories of elements, or domain types. You can define these new types using the existing ones as a base. For example, a product group might identify three main types of reference topic - messages, utilities, and APIs - and define three domains - networking, programming, and databases. By creating a specialized topic type for each kind of reference information, and creating a domain type for each kind of subject, the product architect can ensure that each type of topic has the appropriate structures and content. In addition, the specialized topics make XML-aware search more useful, because users can make fine-grained distinctions. For example, a user could search for xyz only in messages or only in APIs, as well as searching for xyz across reference topics in general.

Rules govern how to specialize safely: Each new information type must map to an existing one, and new information types must be more restrictive than the existing one in the content that they allow. With such specialization, new information types can use generic processing streams for translation, print, and Web publishing. Although a product group can override or extend these processes, they get the full range of existing processes by default, without any extra work or maintenance. The DITA specialization articles outline the rules for each kind of specialization (topic type and domain type).