SOAP

Simple Object Access Protocol (SOAP) is an XML-based messaging protocol for exchanging information among computers. SOAP relies on application layer protocols, most often Hypertext Transfer Protocol (HTTP) or Simple Mail Transfer Protocol (SMTP), for message negotiation and transmission. As we are talking about HTTP, which is installed and runs on every operating system, web services implementing SOAP can be called from any platform using any language.

SOAP structure

We already know that a SOAP message is an XML document, but let's have a better look by way of a diagram:

The following is a description of the components from the preceding diagram:

• Envelope: Mandatory element of SOAP message structure. Defines the start and the end of the message.
• Header: Optional element of the SOAP message. It contains information regarding the SOAP message that can be used to process the data.
• Body: This is the main part, which contains the actual message in XML structure. Obviously, it is a mandatory element...