  We consider a system where the updates from independent sources are
disseminated via a publish-subscribe mechanism. The sources are the publishers
and a decision process (DP), acting as a subscriber, derives decision updates
from the source data. We derive the stationary expected age of information
(AoI) of decision updates delivered to a monitor. We show that a lazy
computation policy in which the DP may sit idle before computing its next
decision update can reduce the average AoI at the monitor even though the DP
exerts no control over the generation of source updates. This AoI reduction is
shown to occur because lazy computation can offset the negative effect of high
variance in the computation time.
