Database Object

dear all, straight to the point... i have this class class Contract { private $id; private $date; private $c_number; -- setter and getter -- } class ContractCME extends Contract { private $tower_height; private $shelter; -- setter and getter -- } class ContractCMD extends Contract { private $type; private $brand; -- setter and getter -- } ok, both CME and CMD are contract, but differ in it's content, one is tower and other is microwave. how to put the class into database ? should i made a contract table , a cme and cmd one... ? any suggestion ? -- Jangan tanyakan apa yang Indonesia telah berikan pada mu tapi bertanyalah apa yang telah engkau berikan kepada Indonesia -----BEGIN GEEK CODE BLOCK----- Version: 3.1 GU/IT d- s: a-- C++ UL P L++ E W++ N* o-- K- w PS Y-- PGP- t++ 5 X R++ tv b+ DI D+ G e+ h* r- z? ------END GEEK CODE BLOCK------