For the past two years there has been a ranging debate among our customers between DITA and DocBook as the XML standard for storage of book content (note: NLM seems more universally accepted among the STM community).
In this debate, DocBook is the incumbent and has been a de-facto standard for more than a decade. DocBook is defined by a RELAX NG schema, with a very mature community and tools including conversion to various other XML formats and HTML.
DITA is the newcomer. DITA (Darwin Information Typing Architecture) is an emerging standard that was approved only in 2005 but has gained momentum because of its extensibility. DITA content uses topic items, each of which are generic enough to map to existing definitions.
But maybe the best XML standard is right in front of us? In fact, you are looking at it right now in this blog.
XHTML has universally been accepted as the standard for online publishing. XHTML can be natively displayed by all major browsers. It is the format supported natively within eBook formats such as EPUB and MOBI. XHTML has excellent support for MathML, linking, and re-use.
There are more than 25,000 international publishers and the majority of these are, in fact, not debating DITA vs DocBook. But they ARE converting to EPUB. As such, while the debate rages on among the world's major publishers, most of the rest of the world's publishers continue to push forward with conversion to XHTML format by way of EPUB.
Implicitly, then, XHTML is already becoming the de-facto standard.