Difference between message bus and message broker

Question

what's the difference between a message bus[1] and a message broker[2]

• Both is middleware for applications
• Both can be used to decouple various systems
• Both can have a canonical data model
• Both route messages and could offer other features such as data transform

As i see, the only relevent difference is the picture used to represent each of one..

If there's some difference between then, please tell-me what.
If they are the same, plese tell-me why two concepts to refer the same functionality.

Thanks.

[1] http://www.eaipatterns.com/MessageBus.html
[2] http://www.eaipatterns.com/MessageBroker.html

Answer 1

The message bus implies a common protocol spoken and understood by all participants. There is little to no logic in the bus. Usually the message is forwarded to all connected systems.

The hub-and-spoke architecture (or "message broker") has a central piece of software which understands the messages sent to it, can translate them, and forward them to the systems which need the information.