SWDB/application/entity/Entity.php

<?php

    /**
     * Entity superclass.
     *
     * Every other entity must inherit from this one. It represents a database
     * entity.
     */
    abstract class Entity{

        /**
         * Database connection.
         */
        public $db;

        /**
         * Constructor.
         *
         * Sets the database conection and the language.
         *
         * @param MySQL_connection $db Connection to the database.
         */
        public function __construct($db){
            $this->db = $db;
        }
    }
?>