References provide quick access to facts. They describe regular features of a subject or product, such as commands in a programming language, ingredients for food recipes, bibliographic lists, etc. The reference is a specialization of the generic topic.
Figure 1. DITA Reference opened in Serna.
Information needed for deeper understanding of a reference topic or to perform related procedures should be provided in a concept or task topic.
You can find more information about reference topics at: http://docs.oasis-open.org/dita/v1.1/OS/archspec/dita_spec_22_info_refs.html.