The next generation application interaction after the message queue is an open standard protocol called web services. It allows applications to communicate based on XML/SOAP/HTTP methodologies for information exchange. A simple individual application can be converted into a web application interacting with other applications using web services.

A web service can be defined as a collection of open protocols and standards for exchanging information among systems or applications. Enterprise applications developed in diverse technologies and languages and executed on different platforms can make web services a common technology to exchange information across system networks (internet/intranet), a kind of interprocess communication within a single computer. This interoperability (for example, between .Net and Java or Linux and Windows) is possible by following open standards.

Not all services performed by an application can be described as a web service. A service can be treated as a web service if:

• The service is discoverable through a simple lookup
• It uses a standard XML format for messaging
• It is available across internet/intranet networks.
• It is a self-describing service through a simple XML syntax
• The service is open to, and not tied to, any operating system/programming language

By following the aforementioned standards, web services attribute the loosely coupled, coarse grained, and synchronous/asynchronous information exchange between applications. Take a look at the following diagram:

SOAP and RESTFUL are the two main types of web service.

The beauty of web services is that you can build them in two ways: either define the interface with which the individual application will implement its application behavior or expose the existing application functionality as a web service. These are termed top-down or bottom-up approaches, respectively.