Shortened, "observability" ("observabilite " in french system theory language) means that you have enough SENSORS. "Controllability" ("gouvernabilite" in french system theory language) means you have enough and coherent ACTUATORS. Put that in a closed loop with a feedback coming to the comparateur, and "pilot " the multivariable difference (we say "piloter l 'erreur " in french)).
It is the center of automation, regulation, robotik, system theory,call it as you want.
RH
