SOAP, is defined as Simple Object Access Protocol. SOAP is a protocol build to simplify the data exchange between applications. It provides the foundation layer for data exchange between applications using xml based web services stack.

SOAP has three major features, one Extensibility - Which allows developers to extend the scope of SOAP using extensions. Second Neutrality - which means SOAP, is platform independent and transport protocol independent hence SOAP can be used on HTTP, SMTP, TCP or JMS transport protocol. Third Independence - SOAP is development platform independent.

SOAP can be used in variety of way for example a stock trading website can send the latest quotes over web services using SOAP. An Insurance company can transfer fraud detection data with other insurance company over SOAP.

SOAP specification define the messaging frame work which consists of SOAP processing model, SOAP extensibility model, SOAP underlying protocol binding,  SOAP message construct.

A SOAP message is a simple XML document with following elements

Envelope - Identifies the XML document as a SOAP message.

Header - Contains header information. 

Body - Contains call and response information.

Fault - Provides information about errors that occurred while processing the message.

Benefits of SOAP:

1. Works on all most all transport protocols

2. It can be used over firewall

Disadvantages of SOAP:

1. Slower than proprietary middle ware

2. Developers must use polling instead of notification.