Associations, aggregations & compositions

[MelodyMaker]

Hi!

I'm a bit confused about the associations between objects, so I would like to ask you about it, by using the following example:

class DatabaseManager{	

private function __construct(){}
private function __clone(){}

static public function getInstance(){
	switch (Configuration::getInstance()->DBMS){
		case "mysql":
			return MySqlDB::DBgetInstance();
			break;
		default:
			return MySqlDB::DBgetInstance();
	}
}
}

Class Configuration{
	private $DBconn 	= "localhost|myUser|myPwd|myDB";
	private $sessionExpiration = 3600;
	private $DBMS = "mysql";
	private static $confInstance;

private function __construct(){}

public static function getInstance(){
	if (!self::$confInstance){
    	self::$confInstance = new Configuration();
	}
	return self::$confInstance;
}  

public function __GET($property){		
	if(isset($this->$property)){
		return $this->$property;
	}
	return false;
}

private function __clone(){}
}

Class MysqlDB{
 private $conf;
 public function __construct(){
  $this->conf = Configuration::getInstance();
  ...
 }

 ...bla bla
}

I just would like to know what kind of association ther is between the configuration and the other two classes. I've just started to draw UML diagrams, and I'm getting mad about it...

Thanks in advance!

Davide

[laserlight]

From what I see, Configuration is a singleton. MysqlDB has a reference to a Configuration, so there is an association between the two classes. Now, we ask: is a Configuration a part of a MysqlDB? This seems to be the case, so the association could be an aggregation. On the other hand, a Configuration can be shared, so it is not just a part of a MysqlDB. Therefore the association is not an aggregation. It is not composition either, since the lifetime of a Configuration object is not tied to its MysqlDB object. (Anyway, composition is a stronger form of aggregation.)

DatabaseManager does not store any references, so there is no association between DatabaseManager and either MysqlDB or Configuration. However, DatabaseManager depends on Configuration and MysqlDB.

[MelodyMaker]

Thank you for your support! So it is a simple One to One association?

[laserlight]

Yes.