Large distributed systems are often overwhelmed with complications caused by heterogeneity and interoperability. Heterogeneity issues may arise due to the use of different programming languages, hardware platforms, operating systems, and data representations. Interoperability denotes the ability of heterogeneous systems to communicate meaningfully and exchange data or services. With the introduction of middleware, heterogeneity can be alleviated and interoperability can be achieved. Middleware is a layer of software between the distributed application and the operating system and consists of a set of standard interfaces that help the application use networked resources and services.

In this chapter, we will cover the following topics:

• Enterprise Messaging System (EMS)
• Asynchronous communication
• Synchronous communication
• Java Messaging Service (JMS)
• The publish/subscribe messaging paradigm
• The Point-To-Point messaging paradigm
• JMS interfaces
• Developing a JMS application
• Publish-Subscribe (Topic) Programming
• Point-To-Point (Queue) Programming
• Web services
• Web service architecture
• SOAP web services
• RESTful web services
• Programming SOAP web services
• Programming RESTful web services
• Enterprise integration patterns