SOAP ( Simple Object Access Protocol )

This is one of the two interfaces which uses the Service-Oriented Architecture logic.  It makes Service-Oriented Architecture be possible with Universal Description Discovery and Integration (UDDI).

What is SOAP?

220px-SOAP.svgSOAP ( Simple Object Access Protocol ) is a client/server based protocol, which uses RPC ( Remote ProcedureCall ) model on distributed applications and the communication of web services. More generally SOAP is XML based rules combination for using the functions over web.

All messages about SOAP is forwarded in XML format and there are three kinds of a SOAP message could be:

  • Calling Method
  • Response message
  • Error message

Structure of a SOAP Message


The one which includes all SOAP messages. The root element of  XML document corresponding SOAP message has to be in it. Envelope element includes Body and Header. In an envelope element, there is always a Body element but, there is no necessity for existing of Header. By SOAP architecture, if there is Header element in Envelope, that must be the first element of the Envelope element”s. In the architectures which uses SOAP, TCP absolutely has to be use as access protocol.


We can think Header element in SOAP messages as HTML standards ( <Head></Head> ). Header part is not directly related to Calling Method part. The information called meta-data is sent with header part.


Body part is the most important part of SOAP message. In this segment, the name and parametric info  of the web method is sent as XML format. However in the Response Message, return value of the method is added to Body part. Writing in XML format of method”s parametric structure is called SOAP Serialization. Lastly, body part also includes some information like the name of error and description.