Managing Complexity: Middleware Explained

A sk a network designer what middleware is, and he’ll characterize it as part of the application. Ask an application designer what it is, and she’ll say it’s part of the OS.Which one is it? Traditionally, most definitions seeking to characterize middleware suggest that it is the software that facilitates remote database access and systems transactions. More recently, the term has come to be associated—somewhat limitingly—with distributed platforms like the Open Software Foundation’s Distributed Computing Environment (DCE) and the Object Management Group’s Common Object Request Broker Architecture (CORBA). And some have loosely applied it to systems as diverse as workflow support environments and even to the Web itself. We believe the essential role of middleware is to manage the complexity and heterogeneity of distributed infrastructures and thereby provide a simpler programming environment for distributed-application developers. It is therefore most useful to define middleware as any software layer that is placed above the distributed system’s infrastructure—the network OS and APIs—and below the application layer. In the distributed-computing model,your enterprise moves applications and data to where they can operate most efficiently: to desktop workstations and to LAN, Web, or remote servers. But dealing with the different protocols and interfaces in a distributed environment can be a nightmare. For instance, to provide basic communication services, programming languages support sockets, which are end points in two-way communication links between two programs running on a network. Sockets require client and server to engage in application-level protocols to encode and decode messages. Designing such protocols is cumbersome and can be prone to error. Middleware is basically an alternative to sockets; it abstracts the communication interface to the level of method invocations. Instead of working directly with sockets, you call a method— rather, you have the illusion of calling a method—on a local object.The arguments of the call are in fact packaged up by your middleware and shipped off to the call’s remote target. In this case, as in others, middleware provides the isolating layer of software that shields you from the complexities of a heterogeneous environment.