A SOAP (Simple Object Access Protocol) message is an XML-based protocol used for exchanging structured information in the implementation of web services. The elements of a SOAP message are standardized and consist of the following components:
1. Envelope
The Envelope element is the root element of a SOAP message and defines the start and end of the message. It indicates that the XML document is a SOAP message. The Envelope element is mandatory and must contain the namespace declaration for the SOAP envelope.
Example:
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<!-- Header and Body go here -->
</soap:Envelope>
The Envelope element can contain two child elements: Header and Body[1][2][3][4][6].
2. Header
The Header element is an optional element that contains application-specific information (like authentication, transaction management, etc.) about the SOAP message. It is used to pass any optional attributes of the message that are used in processing the message, either at an intermediary point or at the ultimate end-point.
Example:
<soap:Header>
<!-- Header information goes here -->
</soap:Header>
The Header element must be the first child of the Envelope element if it is present[3][8].
3. Body
The Body element is a mandatory element that contains the actual SOAP message intended for the ultimate recipient. It includes the XML data comprising the message being sent. The Body element can contain any number of child elements, which are typically application-specific elements.
The Body element must be the second child of the Envelope element, following the Header element if it is present[1][2][3][8].
4. Fault
The Fault element is an optional element that provides information about errors that occur while processing the message. It is used to transmit error and status information within a SOAP message. The Fault element must appear as a child of the Body element if it is present.
