function compute_string_distance( $string1, $string2 ) {
		// Vectors containing character frequency for all chars in each string
		$chars1 = count_chars($string1);
		$chars2 = count_chars($string2);

		// L1-norm of difference vector.
		$difference = array_sum( array_map( array(&$this, 'difference'), $chars1, $chars2 ) );

		// $string1 has zero length? Odd.  Give huge penalty by not dividing.
		if ( !$string1 )
			return $difference;

		// Return distance per charcter (of string1)
		return $difference / strlen($string1);
	}