What is the Middleware

　　Middleware is computer software that connects software components or applications. It is used most often to support complex, distributed applications. It includes web servers, application servers, content management systems, and similar tools that support application development and delivery. Middleware is especially integral to modern information based on XML, SOAP, Web services, and service-oriented architecture.

　　The term middleware is sometimes considered a buzzword.


Definition

　　Middleware is the enabling technology of Enterprise application integration. It describes a piece of software that allows two or more software applications to connect together so that they can exchange data.

　　ObjectWeb defines middleware as "the software layer that lies between the operating system and the applications on each side" of a distributed computing system.


Origins

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


Organizations

　　In addition to the existing vendors updating their wares to address the newly expanded vision, vendors such as Mercator, 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.


Types of middleware

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

• Remote Procedure Call (RPCs) - Client makes calls to procedures running on remote systems. Can be asynchronous or synchronous.
  
  
• Publish/subscribe - This type of middleware monitors activity and pushes relevant information to subscribers.
  
  
• Message Oriented Middleware (MOM) - Messages sent to the client are collected and stored until they are acted upon, while the client continues with other processing.
  
  
• Object Request Broker (ORB) - 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.
  
  
• Other sources include these additional classifications:
  
  - Transaction processing (TP) monitors - Provides tools and an environment for developing and deploying distributed applications.
  
  - 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.