Difference between message bus and message broker

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

Solution 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.

Solution 2:

First recognize that these are made-up terms adopted from existing metaphors, like most domain-specific terms are. Nobody has the authority to define them, rather we are just making this stuff up as we (the industry) goes along.

The broker metaphor works nicely with a hub-and-spoke layout. The bus metaphor works better in a direct addressing situation. What is stopping your client from sending a message to one of a number of brokers sitting on the bus, hub-spoke or otherwise? The definitions of the metaphors starts to get a bit silly.

Figure out what you want to do and choose a product that does it best -- hint: it's probably going to provide features of both so-called bus or broker technologies.