SOA and Web Services

Generally when we talk about SOA, the very first thing that comes to our mind is the web services. Too often, we equate a WebService and its implementation with the overall definition of SOA. In reality it is nothing more than an implementation. A good implementation, but just an implementation. A WebService is platform and language independent and its use of XML enables different platforms to communicate with one another. 

It is not true that every web service is SOA compliant and those Organizations/Companies which implements web services thinking they are implementing SOA, finally end with a total failure.

The world has been implementing SOA long before web services came into existence (you can refer to some case studies of SOA implementation at this link -- Case Studies). Below are few of many protocols which were used to implement SOA:

1. Advanced Program-to-Program Communication (APPC)

Advanced Program to Program Communication or APPC is a protocol which computer programs can use to communicate over a network. APPC is at the application layer in the OSI model, it enables communications between programs on different computers, from portables and workstations to midrange and host computers.

2. Remote Procedure Calls/Remote Method Invocation (RPC/RMI)

A Remote Procedure Call (RPC) is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction. When the software in question uses object-oriented principles, RPC is called Remote Invocation or Remote Method Invocation.

3. Internet Inter-ORB Protocol (IIOP)

IIOP is an object-based protocol and has the potential to massively enhance the types of applications or services or databases that are built and communicate on the web. IIOP provides a comprehensive system through which live objects can request services from one another across the corporate networks over the internet or intranet.

In today's world, when everyone is moving to cloud, the best example of SOA implementation is what Cloud offers as:

A. Software as a Service (SaaS)

B. Platform as a Service (PaaS)

C. Infrastructure as a Service (IaaS)

So, we can say that Web services are just an implementation of SOA but not the only implementation. There are many more examples available on the internet about SOA implementations.