butting in here...
Nick, Saying that the light is green is reporting an observation.
Saying the light is in a green state is making a statement about the
light as a mechanism. As I said, I think of the notion of state as
identifying a collection of functionalities. So attributing a "green
state" to the light implies that when in that state it has a specific
set of functional attributes. Saying that the light is green doesn't
say anything like that.
so, if the light is operated by relays, we can check the position of the
relays to determine the "state" of the green light, but if the light
*bulb* behind the green lense is burned out, is the light in the green
state or not? The relay powering it is. Or do we simply make up
another bit of state for whether the light bulb is operational... and
then another for whether the lens is covered in snow to the point of
being blanked?
For the control-systems engineer designing/building/operating the light
system the first is paramount, the second is valuable but the third is
probably out of scope? To the driver (or the traffic police) all three
sum to one simply point: "what color is the light? (and on a good day,
"can I trust it?").
- Steve
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