gistfile1.php

<?php 
interface Driver
{
    // lo comun que tienen los driver
    public function crearBd();
}

class Mysql implements Driver
{
    //implementas tus métodos
    public function crearBd() 
    {
        //implementa tu metodo
    }
}

class Sql
{
        public function crearBd(Driver $motor) 
}