Teams can see pomsets
Gordon D. Plotkin, Vaughan Pratt · DIMACS series in discrete mathematics and theoretical computer science · 1997
Strings may serve as both specifications and observations of behavior. However partial strings or pomsets, superior to strings in certain respects for the representation of concurrent behavior, are provably unobservable and hence apparently suitable only for specifying behavior. The proof however tacitly assumes that observers are isolated individuals. We show that observations by a cooperating team of sequential observers agreeing on what happened but not when can distinguish all pomsets. The resolving power of a finite team increases strictly with its size k, permitting it to distinguish all pomsets of dimension (not width) k but not all of k + 1. These results extend to observation of augment closed processes. As expected we depend on the now standard technique of refinement of atomic events to complex events; what is not expected is that their complexity need be only that of nondeterminism, in that we refine one atomic event to a set of alternative atomic events, not to a set of sequences.