B2B Integration : A Practical Guide to Collaborative E-commerce

Producer
Topic
t
Middleware Technologies 223
Subscribes
Delivers
Msgl
Delivers
Subscribes
Figure 8.2. — Publish/subscribe messaging system
Subscriber 1
Subscriber 2
'subscribe' to events of interest and consume events (see Figure 8.2).
Producers associate messages with a specific topic and the messaging
system routes messages to consumers based on topics the consumers
register interest in.
Publish/subscribe allows each application in the system to decide
which events it wants to be notified about. Publishers do not know
which applications are subscribing, nor do they care. The messaging
middleware is responsible for ensuring that each subscriber receives the
message once it receives it from the publisher. TIBCO's TIB/Rendezvous
popularized the publish/subscribe model, where it found a large following
in the financial industry.
Point-to-point
In point-to-point messaging systems, messages are routed to an individual
consumer which maintains a queue of 'incoming' messages. Messaging
applications send messages to a specified queue and clients retrieve
messages from a queue.
As Figure 8.3 illustrates, the traditional point-to-point MOM architecture
can create a maintenance nightmare. Each application's messaging
service must know about the messaging services of all other applications
in order to communicate. As new applications are added to the enterprise,
their messaging services must be systematically updated to communicate
with each application.