Refer to figure. 
EASA learning objective 022.12.03.01.03 states: 'List the main components of an SWS.' 
EASA learning objective 022.12.03.01.04 states: 'Explain the difference between the stall warning speed and the actual stalling speed of the aeroplane.' 
EASA CS25.207 states: '(a) Stall warning with sufficient margin to prevent inadvertent stalling with the flaps and landing gear in any normal position must be clear and distinctive to the pilot........' (c) When the speed is reduced at rates not exceeding 0.5 m/s² (one knot per second) stall warning must begin.........by not less than 9.3km/h (five knots) or five percent CAS'.

While many types of aircraft may experience pre-stall buffet as a warning of an impending stall, it's not considered to be sufficiently clear and distinctive enough on large transport aircraft, hence the need for a stall warning system (SWS). Aerodynamic stalling is a result of an excessively high angle of attack (AoA), therefore AoA is the primary input into a SWS. Aircraft configuration is a factor because high lift devices, such as flaps and slats, increase the angle of attack at which the stall occurs so the SWS needs to know wing flap/slat deflection..

Landing gear position does not affect the angle of attack at which a wing stalls so its position is not required as an input however an input is required from the weight on wheels microswitch to inhibit stall warning on the ground.

Given that the airspeed at which the stall occurs varies with factors such as weight, altitude, thrust etc, you might be forgiven for thinking that a SWS has no need of an airspeed input as well as AoA. CS-25 rules dictate that the SWS must give a stall warning not less than 5 knots or 5% of CAS above the stall speed. Therefore to satisfy this rule the SWS needs a CAS input. CAS is IAS corrected for instrument and position error and this is what's output from the air data computer (ADC) to the SWS.

1 – mass of the aeroplane → INCORRECT.  Aircraft mass does not affect the critical angle of attack, the primary input of a SWS is AoA.
2 – angle of attack → CORRECT.  A stall occurs when the wing exceeds its critical angle of attack, regardless of airspeed.
3 – wing flap deflection → CORRECT.  Flaps change the shape of the wing and therefore the angle of attack at which it stalls.
4 – position of the landing gear → INCORRECT.  The position of the gear has no effect on the angle of attack at which a wing stalls
5 – TAT → INCORRECT.  TAT has no effect on the angle of attack at which a wing stalls
6 – pressure altitude → INCORRECT. Pressure altitude has no effect on the angle of attack at which a wing stalls