Simple Object Oriented Protocol or SOAP is a stateless, platform independent, XML based generic lightweight protocol that used HTTP as its transport and can be used for developing distributed complex computing environments.  SOAP is about applications communicating directly with each other over the Internet in a very rich way.  It is a stateless, message exchange paradigm that allows for exchange of data between heterogeneous web applications.  SOAP is supported on any platform and be utilized on a wide variety of applications.  SOAP is similar to its contemporary technologies, like DCOM or CORBA, in the sense that both provide a RPC mechanism for invoking remote methods.  However, SOAP differs from these technologies in the XML Open Standard that it provides for the purpose of data exchange between homogenous or heterogeneous distributed applications.  SOAP is supported by both HTTP and SMTP, but HTTP gained more acceptances over the years.

SOAP is platform independent, language independent and messaging between applications makes this protocol a robust and standardized mechanism in order to handle message communication across homogenous or heterogeneous networks.  The most common messaging pattern used in SOAP is Remote Procedure Call or RPC.  This indicates that the client sends a request message to the server.  The server in turn sends the response message to the client.  The prerequisite for having a proper understanding of SOAP is XML.  This is because XML is the basis of all SOAP related activities.  All SOAP messages are transmitted in XML format.  XML, a platform independent Meta (Language composed of non-binary ASCII text), has revolutionized the way data is transferred between systems.  XML is fast becoming as ubiquitous as HTTP.  It has now already become an accepted standard for representation and interchange of data in structured form accross systems.  All SOAP messages are transmitted as XML.