On 7/19/2011 9:32 AM, Matty Sarro wrote:
Hey everyone. I am currently reading through an RFC, and it mentions that a client and server half of a transaction are embodied by finite state machines. I am reading through the wikipedia article for finite
That was going to be my first suggestion, but I see that it is flagged as possibly confusing. You *might* find the article on Turing machines more helpful, as they are finite-state machines that compute, and the base model for digital (as opposed to analog) computers.
state machines, and sadly it's going a bit above my head. I don't really have a background in engineering, and would really love to understand what is being said. Does anyone have a simple way to explain it?
You did not say what background you do have, so I will assume you are familiar with cars and light switches. The piston chamber in a car engine has several continuous variables. Temperature, pressure, concentration of nitrogen, oxygen, fuel, and combustion products, and position and velocity of the piston. It is a continuous-state machine.
A lamp switch, on the other hand, is the simplest-possible useful finite state machine. It has two states (on and off) and just one input (rotate) that switches between the two. A vertically mounted wall light switch has two inputs (push-up and push-down) that each either switch the state or leave it the same.
Back to cars. The transmission is a finite-state machine. It has a small finite set of gear settings: P, R, N, D, D2, L (for one example). The inputs are pushes (push right-left, up-down, or maybe both) on a gear stick that either switches to another state or stays in the original state. Ignition key settings are similar. In modern cars, the two are interlinked. For automatic transmissions, there is the additional complication that switching from N to D while stationary actually switches from N to L, and gear switch inputs are generated by the car as well as by the driver.
The common feature of finite state machines are finite sets of states, inputs, and outputs. Inputs may cause a switch to another state and an output. Another everyday example: a house door can be open, closed, locked, dead-bolted, or both, and maybe barred. There are input actions but no outputs, unless the door is hooked to an alarm system, which is another finite-state system.
-- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
