static function removeById( $attributeId, $version = null )
    {
        if ( $version !== null )
    	   $conds = array( 'contentobject_attribute_id' => $attributeId, 'contentobject_version' => $version  );
    	else
    	    $conds = array( 'contentobject_attribute_id' => $attributeId );

        eZPersistentObject::removeObject( self::definition(), $conds, null );
    }