Transition Diagram for Watcher
If user clicks on a multimedia document such as a web page,
a message m1 is sent to the Watcher, which
transits from state S0 to state S1,
sends a null message m0 (i.e., no output message)
and performs action a1 to update usage frequency.
If the Prefetcher sends a message m2 to the
Watcher to request information, it should be already
in state S1 and will remain in that state. The Watcher responds by sending
a message m3 back to the Prefetcher
and performing action a5
to update request frequency.
