On Java Message Services...

Keywords
message server: message broker, message router
message-oriented middleware
message: self-contained package of business data and network routing header

enterprise messaging: allows two or more applications to exchange information in the form of messages

MOM usually provides fault tolerance, load balancing, scalability (clustering), and trasactional support.

messaging system = message clients + MOM

centralized vs decentralized architecture

in centralized architecture, the message server may be a cluster of distributed servers operating as a logical unit.

important note: client only sees the message server (the destination) and not other clients. the server will then dispatch the messages to the clients who subscribe to the same topic or queue. in this way, the senders and the receivers are decoupled and maybe added or removed from the system. also, any failure in a particular part of the system will not affect the functioning of other parts of the system.

think of JMS as a facade pattern. (Most APIs are facade patterns)

hybrid architecture