I think it might be a good idea to have a database table for plugins.

If plugins needs to store some values currently this is done
mostly by using 'users' table 'preferences' field.

CREATE TABLE IF NOT EXISTS `plugins` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`contact_id` int(11) DEFAULT NULL,
`identity_id` int(11) DEFAULT NULL,
`plugin` text,
`key` text,
`value` text,
`timestamp` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
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