All major airlines and most of the minor ones are in all GDS systms. Most hotels are in all GDS systems. When using these you view and book directly into actual availability for airlines, hotels, cars, amtrak and other vendors. There is a special and complicated language used by each GDS which is not interchangeable. You have to pay for access and you have to know what you are doing. In order to gain access you would have to contact the system (Sabre, Amadeus, Appollo or Worldspan) and see what you would have to pay.