  Complex systems are often composed of many small communicating components
called modules. We investigate the synthesis of supervisory controllers for
modular systems under partial observation that, as the closed-loop system,
realize the supremal normal sublanguage of the specification. We call such
controllers maximally permissive normal supervisors. The challenge in modular
systems is to find conditions under which the global nonblocking and maximally
permissive normal supervisor can be achieved locally as the parallel
composition of local normal supervisors. We show that a structural concept of
hierarchical supervisory control called modified observation consistency (MOC)
is such a condition. However, the algorithmic verification of MOC is an open
problem, and therefore it is necessary to find easily-verifiable conditions
that ensure MOC. We show that the condition that all shared events are
observable is such a condition. Considering specifications, we examine both
local specifications, where each module has its own specification, and global
specifications. We combine our results for normality with the existing results
for controllability to locally synthesize the nonblocking and maximally
permissive controllable and normal supervisor. Finally, we illustrate the
results on an industrial case study of the patient table of an MRI scanner.
