Soap is a formatting protocal.
When we send data to the webservice the data will be passed 
in network wire.
That data has to formatted by SOAP. and sends to the 
service.
then the service will give response to that request . This 
data is also formatted by Soap and give it to the client.

SOAP--> HTTP + XML

The format is XML because it is platform dependent . this 
service is used by other applications .