What role do DTDs (Document Type Definitions) and schemas play in DITA specialization?

Document Type Definitions (DTDs) and schemas are foundational elements in DITA specialization, playing a critical role in defining the structure, constraints, and rules for specialized content. Here’s how DTDs and schemas contribute to DITA specialization:

Structure Definition

DTDs and schemas define the allowable structure for DITA documents, including topics, maps, and specialized elements. They specify the hierarchy of elements, the order in which elements can appear, and the relationships between elements. For specialization, this means that DTDs and schemas enable you to create new specialized elements and establish where and how they can be used within your content. This control over content structure is essential for ensuring consistency and adherence to your organization’s content standards.

Constraint Enforcement

DITA specialization often involves imposing constraints on the content to ensure it complies with specific requirements. DTDs and schemas allow you to enforce these constraints by defining rules for elements and attributes. For example, you can limit the values that certain attributes can have or specify that particular elements are required. These constraints help maintain content quality and consistency, which is especially crucial when multiple authors are contributing to the content or when content is being translated into multiple languages.


DTDs and schemas play a pivotal role in the validation process. Content authored in DITA is typically validated against a DTD or schema to ensure it meets the defined rules and constraints. This validation process helps identify errors, inconsistencies, or non-compliance with the specialization guidelines. By using DTDs and schemas, organizations can have confidence that their specialized DITA content remains structurally sound and consistent, even as it evolves over time.


Here’s an example of how DTDs and schemas are used to define constraints for a specialized DITA element:

<!ELEMENT <specialized-element> (child-element)*>
<!ATTLIST <specialized-element>
  custom-attribute (value1 | value2) #REQUIRED

In this example, a DTD snippet is defining a specialized element named <specialized-element>. It specifies that this element can have zero or more <child-element> elements and enforces that the attribute custom-attribute must have a value of either value1 or value2 and is required. This is just one way DTDs and schemas can be used to define specialized content structures and constraints in DITA.