The era of isolated computers is over. Now "connected we stand, isolated we fall" is becoming the motto of computing. Networking and communication facilities have connected the world in a way as never before. The world has hardware that could support the systems that connect thousands of computers, and these systems have the capacity to wield power that was once only dreamed of.

Yet, computer science lacked the technologies and abstraction to utilize the established communication networks. The goal of distributed computing is to provide such abstractions. RPC, RMI, IIOP, and CORBA are a few proposals that provide abstractions over the network for the developers to build upon.

These proposals fail to consider one critical nature of the problem. The systems are a composition of numerous heterogeneous subsystems, but these proposals require all the participants to share a programming language or a few languages. Service Oriented Architecture (SOA) provides the answer by defining a set of concepts and patterns to integrate homogenous and heterogeneous components together. SOA provides a better way to achieve loosely coupled systems, and hence more extensibility and flexibility. In addition, similar to object-oriented programming (OOP), SOA enables a high degree of reusability. There are three main ways one can enable SOA capabilities in their systems and applications:

Among the commonly used messaging systems, Java Messaging Service (JMS) plays a major role in the industry and has become a common API for messaging systems. We can find a number of different message types of JMS, such as Text, Bytes, Name-Value pair, Stream, and Object. One of the main disadvantages of these types of messaging systems is that they do not have a single wire format (serialization format). As a result, interoperability is a big issue: if two applications are using JMS to communicate, then they must be on the same implementation. Sonic, Tibco, and IBM are the leaders in the commercial markets, and JBoss, Manta, and ActiveMQ are the commonly used open source implementations.

Plain Old XML or POX is another way of exposing functionality and enabling SOA in the system. With the widespread use of the Web, the POX approach has become more popular. Most of the web applications expose the XML APIs, where we can develop components and communicate with them. Google Maps, Auto complete, and Amazon services are a few examples of applications that heavily use XML APIs to expose the functionality. In most cases, POX is used in combination with REST (Representational State Transfer). REST is a model of an underlying architecture of the Web, and it is based on the concept that every URL identifies resources. GET, PUT, POST, and DELETE are the verbs that are used in the REST architecture. REST is often associated with the theoretical standpoints, and for this reason, REST is generally not used for complex interactions.

Among the three commonly used methods to enable SOA, a web service can be considered as the most standard and flexible way. Web services extend the idea of POX and add additional standards to make the communication more organized and standardized. There are several reasons behind the web services being the most popular SOA-enabled mechanism, as stated here: