SOAP Messages

Let's take a look at an example of a SOAP message and examine the individual parts of the message.  Keep in mind that a SOAP message is an XML document, it just adheres to the SOAP message schema.  

The Envelope must be the first element in a SOAP message.  It identifies an XML document as being a SOAP message and encapsulates all the other parts of a message.  The Envelope contains the version information about the message, and it identifies the rules used by the application to serialize data.  Both the version and encoding rules are represented as namespace URIs in the Envelope.

After the Envelope, a SOAP message can contain a Header element.  The Header element is optional and can be used to extend the message syntax independently from a particular application.  For example, information could be added to the Header element to add authorization or transaction information to a message.  If a Header appears, it must immediately follow the Envelope.

The Body element is the area of a SOAP message where the application-specific data is placed.  In the example message below, the SOAP Body represents a remote procedure call to the method DoCreditCheck.  The encoding rules of the Envelope element describe what syntax was used to encode data in the Body.  The next page deals with how that data is represented in more detail, but the Body element can hold any XML that your application needs to send or receive through messages.

The example message below shows how the Envelope, Header, and Body are used to build a complete message.  Move your mouse over the message below and you can see each part separately.

The XML above shows you what a SOAP message should look like.  But how does a message get from one application to another, and what should be in the payload?  The next page deals with some of those issues.