Create an XML schema for a catalog of cars, where each car has the child elements make, model, year, color, engine, number_of_doors, transmission_type, and accessories. The engine element has the child elements number_of_cylinders and fuel_system (carbureted or fuel injected). The accessories element has the attributes radio, air_conditioning, power_windows, power_steering, and power_brakes, each of which is required and has the possible values yes and no.