Use an xref or link element in your text to form an active link to one of the entries in your document's bibliography. If you are using version 4.4 of the DocBook DTD, you can also use biblioref. Each of these requires putting an id attribute value on the biblioentry or bibliomixed element in the bibliography, and using that value as the linkend attribute value in the xref, link, or biblioref element.

The citation element can also be used, but it does not form an active link to the bibliography. The element's text content is just displayed inside square brackets. You can use citation when you don't want an active link, or if the reference is not in your current bibliography.

If you use an xref or biblioref element, then text will be generated for the citation. The generated text depends on several factors, shown here in the order in which they are considered.

For example:

This citation:
<xref  linkend="BrodyArticle"/>

to this entry:
<biblioentry  id="BrodyArticle">
  <abbrev>brody98</abbrev>
  <author>...
</biblioentry>

will generate this citation text:
[brody98]

If there were no abbrev child, then the id value would be used, so in this case it would produce [BrodyArticle].