Middleware is software that makes it possible to build distributed applications. Middleware allows processes in different address spaces to communicate.

Middleware should provide the following:

• Ease of use
  Middleware should be easier to use than writing a low level communication interface using sockets.

• Location transparancy
  It should be possible to move an application to a different network address without the need to recompile any software.

• Message integrity
  Messages should not be lost or duplicated and their contents should not be corrupted. This is usually provided by network software such as TCP/IP.

• Language transparancy
  A process using the middleware should be able to communicate with a process that was written with a different language.

Middleware Elements (Top)

Figure 1: Middleware Elements

Middleware Categories (Top)

We will separate middleware into two broad catagories:

• Application Middleware
  Application middleware is used to connect a process in one address space to a process in another address space, usually using a client server style. The connection may be from an actual client to an actual application server or from one application server (acting as a client) to another application server.

• Database Middleware
  Database middleware is used to connect a process in one address space to a database in another address space, usually using a client server style. Database middleware often uses some of the same technology as application middleware.