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Middleware is computer software that connects software components or 
applications. The software consists of a set of enabling services that 
allow multiple processes running on one or more machines to interact across 
a network. This technology evolved to provide for interoperability in 
support of the move to coherent distributed architectures, which are used 
most often to support and simplify complex, distributed applications. It 
includes web servers, application servers, and similar tools that support 
application development and delivery. Middleware is especially integral to 
modern information technology based on XML, SOAP, Web services, and 
service-oriented architecture.

sits "in the middle" between application software working on different 
operating systems. It is similar to the middle layer of a three-tier single 
system architecture, except that it is stretched across multiple systems or 
applications. Examples include database systems, telecommunications 
software, transaction monitors, and messaging-and-queueing software.

The distinction between operating system and middleware functionality is, 
to some extent, arbitrary. While core kernel functionality can only be 
provided by the operating system itself, some functionality previously 
provided by separately sold middleware is now integrated in operating 
systems. A typical example is the TCP/IP stack for telecommunications, 
nowadays included in virtually every operating system.

In simulation technology, middleware is generally used in the context of 
the high level architecture (HLA) that applies to many distributed 
simulations. It is a layer of software that lies between the application 
code and the run-time infrastructure. Middleware generally consists of a 
library of functions, and enables a number of applications �C simulations 
or federates in HLA terminology �C to page these functions from the common 
library rather than re-create them for each application

Contents [hide]
1 Definitions
2 Origins
3 Organizations
4 Use of middleware
5 Types of middleware
6 See also
7 References
8 External links
 

[edit] Definitions
Middleware is the enabling technology of enterprise application 
integration. It describes a piece of software that connects two or more 
software applications, allowing them to exchange data.

ObjectWeb defines middleware as: "The software layer that lies between the 
operating system and applications on each side of a distributed computing 
system in a network."[1]


[edit] Origins
Middleware is a relatively new addition to the computing landscape. It 
gained popularity in the 1980s as a solution to the problem of how to link 
newer applications to older legacy systems, although the term had been in 
use since 1968.[2] It also facilitated distributed processing, the 
connection of multiple applications to create a larger application, usually 
over a network.


[edit] Organizations
IBM, Red Hat, and Oracle Corporation are major vendors providing middleware 
software. Vendors such as SAP, TIBCO, Mercator Software, Crossflo, Vitria 
and webMethods were specifically founded to provide Web-oriented middleware 
tools. Groups such as the Apache Software Foundation and the ObjectWeb 
Consortium encourage the development of open source middleware.


[edit] Use of middleware
Middleware services provide a more functional set of application 
programming interfaces to allow an application to:

Locate transparently across the network, thus providing interaction with 
another service or application
Be independent from network services
Be reliable and available always
when compared to the operating system and network services.

Types of middleware
Hurwitz's classification system organizes the many types of middleware that are currently available.[3]. These classifications are based on scalability and recoverability:

Remote Procedure Call �� Client makes calls to procedures running on remote systems. Can be asynchronous or synchronous.
Message Oriented Middleware �� Messages sent to the client are collected and stored until they are acted upon, while the client continues with other processing.
Object Request Broker �� This type of middleware makes it possible for applications to send objects and request services in an object-oriented system.
SQL-oriented Data Access �� middleware between applications and database servers.
Embedded Middleware �� communication services and integration interface software/firmware that operates between embedded applications and the real time operating system.
Other sources include these additional classifications:

Transaction processing monitors �� Provides tools and an environment to develop and deploy distributed applications.[4]
Application servers �� software installed on a computer to facilitate the serving (running) of other applications.
Enterprise Service Bus �� An abstraction layer on top of an Enterprise Messaging System. 
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