PHP Klasse zur MySQL Verbindung - Verbesserungen

<?php

class db_connection {
	var $credentials = array();
	var $credentials['host']     = 'localhost';
	var $credentials['user']     = 'test_user';
	var $credentials['password'] = 'wambo';
	var $credentials['database'] = 'test';

	var $connection_id;
	var $result;
	var $result_code;
	var $state = 'disconnected';
	var $errorcode;
	var $errormessage;

	function db_connection_error() {
		$this -> state        = 'disconnected';
		$this -> errorcode    = mysql_error();
		$this -> errormessage = mysql_errno();
		return 0;
	}
	
	function db_connection_build {
		if($this -> state != 'disconnected') {
			if(!$this -> connection_id =
			mysql_connect($this -> credentials['host'], credentials['user'], credentials['password'])) {
				db_connection_error();
			} else {
				return 1;
			}	
		} else {
			$this -> state = 'connected';
			return 1;
		}	
	}
	
	function db_connection_database() {
		if($this -> state == 'connected') {
			if(!mysql_select_db($this -> credentials['database'])) {
				db_connection_error();
			} else {
				return 1;
			}
		} else {
			return 0;
		}
	}
?>

<?php
class DbConnection //Camelcaps schreibt sich besser
{
// Variablen, Funktionen etc.  typ geben (public, private, protected)
    private $_host = 'localhost'; // evtl sogar protected da ja niemand außerhalb darauf zugreifen soll, außer die klasse selbst
    private $_user = 'testuser';
    private $_pw = 'pw';
    private $_db = 'db';

    public function dbError()
    {
         // bla
    }
    // usw.
}