What is a topic?

A topic in DITA is an independent chunk of information covering a single idea or task, authored as a unit, and stored in its own file. Topics are categorised by information type. DITA's topic-based architecture enables the same topic to be used in different publications.

DITA is designed around a topic-based information architecture; topics are the building blocks of DITA documents. The topic-based approach in DITA is similar in many ways to the topic-based approach of most hypertext systems.

The DITA Architectural Specification defines a topic as follows:
A topic is a unit of information with a title and content, short enough to be specific to a single subject or answer a single question, but long enough to make sense on its own and be authored as a unit.

The DITA approach is that the author writes a topic independently of the publication in which it may eventually be published. (A publication is created by assembling topics into a hierarchical structure and "publishing" the collection of topics to a reading format.) This topic-oriented writing is a disciplined approach to writing that emphasises modularity and re-use of concise units of information.

A topic is created as a standalone chunk of information, typically limited to one idea. A well-written topic will fully convey that idea in one reading. Technically, a DITA topic can be as minimal as just a title, but practically that can only occur when the title alone conveys the idea completely. A topic is stored in its own file. Topics are categorised into different information types.

Although topics can technically be broken down into sections, you must take care to ensure that sections are not used as an alternative to topics. Sections should only be used where the single idea being conveyed in the topic is complex. Using sections instead of topics detracts from modularity.

Note: A number of DITA (source) topics can be later assembled into a single deliverable topic, such as an XHTML topic. DITA includes a chunk attribute for this purpose. You should not create topics in DITA according to how you want the information chunked in the deliverable reading format.