Ben php yeni ve şu anda ben Wrox Profesyonel PHP 5 okuyorum duyuyorum.

Herkes bana aşağıdaki kodu açıklayabilir misiniz?

<? php

abstract class PropertyObject
{
//Stores name/value pairs that hook properties to database field names
protected $propertyTable=array();

//List of properties that have been modified.
protected $changedProperties=array();

//Actual data from the database.
protected $data;

//Any validation errors that might have occured.
protected $errors=array();

public function __construct($arData)
{
     $this->data=$arData;
}

function __get($propertyName)
{
     if(!array_key_exits($propertyName,$this->propertyTable))
     {
          throw new Exception("Invalid property \"$propertyName\" !");
     }

     if(method_exists($this,'get'.$propertyName))
     {
          return call_user_func(array($this,'get'.$propertyName));
     }
     else
     {
          return $this->data[$this->propertyTable[$propertyName]];
     }
}

function __set($propertyName,$value)
{
     if(!array_key_exits($propertyName,$this->propertyTable))
     {
          throw new Exception("Invalid property \"$propertyName\" !")
     }

     if(method_exits($this,'set'.$propertyName))
     {
     return call_user_func(array($this,'set'.$propertyName),$value);
     }
     else
     {
     //If the value of the property really has changed and it's not already in the changedProperties array, add it.

          if($this->propertyTable[$propertyName] !=$value && !in_array($propertyName,$this->changedProperties))
          {
               $this->changedProperties[]=$propertyName;
          }

          //Now set the new value
          $this->data[$this->propertyTable[$propertyName]]=$value;

     }
}

}
?>

Ben değerlendirici içinde kod almak ve yöntemleri ayarlayabilirsiniz anlayamıyorum.