DocBook is an XML schema (language) that has been under development since 1991. It is used by publishers around the world as a preferred schema for single-source publishing of books and technical documents. One such publisher is ANU E Press, which uses DocBook to produce publications. The XML elements of DocBook are terms familiar to editors and publishers—such as book, chapter, glossary, index, bibliography, title, caption, section and paragraph. This naming convention makes it easy for editors to understand how content should be marked up.
The most recent version, DocBook 5, was released in November 2010, and the stylesheets and schema are still being developed by a small group of dedicated programmers to accommodate publishing of new ebook products—PDF, epub 2 and XHTML 1.1 compliant documents can be produced. A new version, DocBook Publishers Schema, is being developed and will better accommodate Dublin Core metadata elements for epub ebooks. Because DocBook is actively maintained and supported with customisable stylesheets, we're confident that it's appropriate for book-based publishing.
An alternative schema is DITA (Darwin Information Typing Architecture). This is newer than DocBook and has a lot of support from technical communication specialists. It is also integrated into various XML authoring products. DITA has a different element structure, and is most suitable for writing online help documentation for software because its content structure is based on standalone, modular topics.