Lesson 3	Message-oriented middleware
Objective	Describe the function of message-oriented middleware

What is message-oriented middleware?

Message-oriented middleware, also known as MOM, provides rules-based message routing capabilities. Typically, message-oriented products offer a basic set of commands with which to communicate over a network. Application developers create application-specific functions or routines built on top of these basic functions. The message-oriented API^[1] is provided for whatever network transports are actually supported by the vendor, not just one single protocol. MOM is based on a peer-to-peer relationship between message queues^[2] that are managed by a common broker. Message-brokering technology enables request-and-reply constructs to be handled asynchronously, which guarantees the delivery and integrity of messages between applications and components.

MOM's publish-and-subscribe model

Newer forms of MOM use the publish-and-subscribe model for message and application brokering. Publish-and-subscribe allows applications and components to communicate and exchange information with ease, chiefly because the components' physical location and identity are transparent to one another. This lends many benefits to users of MOM, which are explained in the table below.

How publish-and-subscribe works	Advantage
It allows applications and components to communicate and exchange information easily, as the components' physical location and identity are transparent to one another.	The services to both parties can be fulfilled without their knowing the routing involved.
	Publishers (message stores) and subscribers (message users) may be deployed dynamically and in various numbers.
	Security is flexible, allowing each unique publish/subscribe pair to implement security that is appropriate to their unique relationship.

In the next lesson, you will learn about RPCs.

[1]API: A set of routines, protocols, and tools for building software applications. Good APIs make it easier to develop a program by providing all needed building blocks.

[2]Message queue: Some messaging systems use a temporary storage facility, called a message queue, to store messages indefinitely. A message queuing system enables applications to communicate even though they may not be running at the same time.

[3]Message-brokering technology: Technology that acts as a message server being multiple systems/solutions requiring integration.