Observation Equivalence

ObservationEquivalence is an idea that arose in Concurrency theory. It was the response to the question `` when are two (concurrent) programs equivalent? .

The answer is that this depends on the observer that interacts with the program. If an observer can interact with two observed entities in such a way that it can spot difference in their behavior, then they are not relatively equivalent.

Now, if you are given a language in which observers can be described, and you can show that for all possible observers two entities exhibit the same behavior, then we have a stronger equivalence, often called congruence. -- AamodSane