abstract class DataSource implements Iterator
{
	public
		$source_name;

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

	// Returns the current data row
	abstract public function current();

	// Returns a key for the current data row
	public function key() {}

	// Advances the current data; no return value
	abstract public function next();

	// Resets the current data to the first value; no return value
	abstract public function rewind();
	
	// Returns true if current() will return valid data
	abstract public function valid();
}