Simple Object Access Protocol
It is preferred way to encode information such as data 
values before sending it to or from a webservice...

Simple Object Access Protocol (SOAP) is a protocol used for 
messaging and it is completely XML based. 
SOAP specifications are standardizes by W3C. 
SOAP provides a complete set of rules for the messages, 
also called SOAP envelopes, as well as rules for issues 
like data encoding, handling of messages, and binding of 
messages to other protocols,such as HTTP. A SOAP message is 
a simple XML document, which always contains a mandatory 
envelope and body element and can also contain a few 
optional elements such as header and fault element.
syntax of SOAP message: 
<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingstyle="http://www.w3.org/2001/12/soap-
encoding">
<soap:Header>
...
...
</soap:Header>
<soap:Body>
...
<soap:fault>
...
</soap:fault>
</soap:Body>
</soap:Envelope>