Kamailio supports multiple database servers in the SQL and also NoSQL area.
Maintaining database schema for each database separately would be tedious job,
therefore Kamailio keeps the database schema in an XML-based format and schema
definitions for the database servers are generated automatically using
stylesheets.

This directory contains DTD (Document Type Definition) files describing the
structure of the XML-based database description language and XSL stylesheets
used to generate database schema files for all the database servers.
