Messaging middleware holds the data in a message queue when the target application is unable to accept it because the server is down or overloaded. There are two major types of messaging transports. IBM's MQSeries has been the leader in the messaging-transport field. Microsoft's MSMQ provides a Windows solution. Neon's e-Biz Integrator and Tibco's Rendezvous are other examples more widely known as message brokers.
Message brokers add routing intelligence and reformatting capabilities to the transport mechanism.
Products are being developed from the get-go that provide integration, brokering and business logic. Active Software's ActiveWorks is one example that has hooks into just about everything. Object Lessons Object request brokers and remote procedure calls are also called middleware, because they send requests to software residing on computers in the network and manage the delivery of the responses. This is like messaging middleware in that they have to manage requests, but also very different because the requests are for executing remote processes rather than sending data. DCOM is a Windows-centric solution, and EJBs are Java based, which by Java's nature means that the software can run on any hardware platform.