Much of the data we see in Joomla! is stored in the database. A base installation has over thirty tables. Some of these are related to core extensions and others to the inner workings of Joomla!.
There is an official database schema, which describes the tables created during the installation. For more information, please refer to: http://dev.joomla.org/component/option,com_jd-wiki/Itemid,31/id,guidelines:database/.
A tabular description is available at: http://dev.joomla.org/downloads/Joomla15_DB-Schema.htm.
We access the Joomla! database using the global JDatabase object. The JDatabase class is an abstract class, which is extended by different database drivers. There are currently only two database drivers included in the Joomla! core, MySQL and MySQLi. We access the global JDatabase object using JFactory:
$db =& JFactory::getDBO();