6. The Enterprise Service Bus is:
a) Another word for middleware
b) A commercial product sold by IBM
c) An event-driven approach to handle messages and workflows
d) More proficient in possibilities than a classical middleware
The ESB is indeed another evolutionary step in middleware and message-handling technology. It is not a product as such, but a different approach to manage message and message flows. Classical middleware acts as an active message broker. This means that all processing logic including the routing information is stored and held by the middleware software. A bus works different as it does not actively process messages but orchestrates its flow only. In order to act upon messages components need to subscribe to the bus to receive the message when they arrive.
The great advantage of the ESB is that it can be installed step-by-step. First you install the ESB infrastructure then you start routing current peer-to-peer communications through the bus. Then you add agents that inspect the messages on the bus and do appropriate enhancements or filtering. So you could install middleware without having the need for big-bang projects. A classical middleware is much less proficient by design. Unfortunately XI still belongs to the classical category. We expect this to change eventually.
This was first published in September 2005