PluXml is a blog/CMS storing data in XML and not in a SQL database.
Plugins and themes should respectively be installed in the following folders : /var/www/pluxml/plugins, /var/www/pluxml/themes.
To restore your blog, you should keep a copy of the folder /var/www/pluxml/data. It is recommended to do this backup before any upgrade.
PluXml : https://www.pluxml.org/
Documentation : https://wiki.pluxml.org/
Forum : https://forum.pluxml.org/