The ActionBazaar shipping request forwarding was implemented using the PTP model. A
request to ship a winning bid should be processed by only one shipper.
Publish-subscribe (pub-sub) messaging is similar to a traditional home-delivered newspa-
by any number of consumers who happen to be connected to the destination at the time. The
message destination in this model is called a topic and a consumer is called a subscriber .
Pub-sub messaging works particularly well in broadcasting information across systems.
For example, it could be used to broadcast a system maintenance notification several hours
before an outage to all premium sellers whose systems are directly integrated with Ac-
tionBazaar and who are listening at the moment.
Figure 4.5. The pub-sub messaging model with one producer and three consumers. Each topic subscriber receives
a copy of the message.