Topic structure

All topics have the same basic structure, regardless of topic type: title, description or abstract, prolog, body, related links, and nested topics.

All DITA topics must have an ID and a title. Topic structures can consist of the following parts:
Topic element
Required id attribute, contains all other elements
Title
The subject of the topic.
Alternate titles
Titles specifically for use in navigation or search. When not provided, the base title is used for all contexts.
Short description or abstract
A short description of the topic, or a longer abstract with an embedded short description. The short description is used both in topic content (as the first paragraph), in generated summaries that include the topic, and in links to the topic. Alternatively, the abstract lets you create more complex introductory content, and uses an embedded short description element to define the part of the abstract that is suitable for summaries and link previews.
While short descriptions aren't required, they can make a dramatic difference to the usability of an information set, and should generally be provided for all topics.
Prolog
Container for various kinds of topic metadata, such as change history, audience, product, and so on.
Body
The actual topic content: paragraphs, lists, sections - whatever the information type allows.
Related links
Links to other topics. When an author creates a link as part of a topic, the topic becomes dependent on the other topic being available. To reduce dependencies between topics and thereby increase the reusability of each topic, authors can use DITA maps to define and manage links between topics, instead of embedding links directly in each related topic.
Nested topics
Topics can be defined inside other topics. Nesting can result in complex documents that are less usable and less reusable, and should be used carefully. It is more often appropriate for reference information, which can support longer documents organized into multiple topics for scanning and retrieval. The rules for nesting topics can vary from document type to document type: for example, the concept document type allows nesting of other concepts only, while the ditabase document type allows nesting of any of the standard DITA topic type.