Bibliography support is currently implemented for DocBook SGML and XML documents, TEI and TEILite XML documents, and for LaTeX documents.
Bibliographic output for DocBook works with both the SGML and XML version of the DTD. The DocBook output is sufficiently structured to allow transformation into other SGML or XML document types (this is in fact the way how the TEI bibliographies are created currently). DocBook SGML and XML documents can be transformed with DSSSL and XSL stylesheets, respectively, which act as driver files for the well-known modular stylesheets by Norm Walsh.
The TEI camp has apparently completely switched from SGML to XML, so RefDB supports only XML documents and transformation with XSL stylesheets.
The implementation of the SGML/XML citations and bibliographies is "non-destructive", i.e. refdb leaves the source document alone and provides all necessary information in a file that can be included into the main document as an external entity. This way, switching from one bibliographic output format to a different one is limited to re-creating this external file without any changes in your source document.
Alternatively you may use a short notation for your citations that makes do with a minimum of markup. The short notation needs an additional (but fully reversible) preprocessing step before bibliographies and formatted output can be created.
refdb uses "cooked" DocBook bibliography output. This somewhat blurs the distinction between structure and formatting but it is the most efficient way to handle the task of formatting bibliographies and citations. The TEI bibliography output is even worse as it heavily abuses the all-purpose seg element as a wrapper where the elements intended for a particular purpose do not allow a "cooked" use.
The BibTeX output integrates seamlessly with the LaTeX/BibTeX tools, so there is only one additional command to run on your way from the LaTeX source to the finished document.
refdb creates a BibTeX bibliography file based on the information in a .aux file. The latter is created by latex from the LaTeX source document. This intermediate bibliography file serves as the input file for bibtex. So instead of keeping all your references in a flat text file, refdb will create a short bibliography file with the references that your particular document requires.
refdb performs only a very limited amount of formatting for those items which are not well supported in BibTeX (e.g. with BibTeX you need two separate bibliography files if you switch from a format that uses abbreviated journal names to a format that requires the full names). All other formatting is left to the LaTeX/BibTeX system.