Distributed Applications that can support heterogeneous platforms for the purpose of data and information requires a common data format for transmission of data.  We have had protocols earlier like DCOM, RPC, IIOP, etc, but these were restricted to a homogenous environment only. They have been around for quite some time now, but they have their own limitations.  Any two systems communicating with each other using any of these protocols should have support for the protocol that they are using.  As an example, if a system "A" communicates with a system "B" using IIOP, both these systems should have support for IIOP to ensure that the communication takes place successfully.  For a heterogeneous environment this is not feasible.  The situation is more complex.  Simple Object Oriented Protocol (SOAP) is an Open Standard protocol and the solution to this complexity.