Distributed objects are considered middleware because they facilitate inter-application communications. Distributed objects are really small application programs that use standard interfaces and protocols to communicate with one another. Thus, distributed objects provide coupled application integration features. Message brokers represent the nirvana of EAI-enabled middleware. At least that's the way they are being sold.
Message brokers can also join many applications using common rules and routing engines.
They can transform the schema and content of the information as it flows between various applications and databases. Message brokers are servers that broker messages between two or more source or target applications. In addition to brokering messages, they transform message schemas and alter the content of the messages so the messages make sense to the application receiving the message. In contrast to application servers, message brokers tend to move information using event-driven mechanisms. Application servers, by contrast, use a transactional model where transactions are invoked within the application server.