Chapter 8 • Web
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• A binding to HTTP, to ensure that the XML message is transported correctly • The conventions for conveying an error in message processing back to the sender
8.2.1 The SOAP Message Format
A unit of communication in SOAP is a message. A SOAP message is an ordinary XML document containing the following elements Figure 8-3:
• A required Envelope element that identifies the XML document as a SOAP message • An optional Header element that contains the message header information; can include
any number of header blocks simply referred to as headers; used to pass additional processing or control information e.g., authentication, information related to transaction
control, quality of service, and service billing and accounting-related data
• A required Body element that contains the remote method call or response information; all immediate children of the Body element are body blocks typically referred to simply
as bodies • An optional Fault element that provides information about errors that occurred while
processing the message SOAP messages are encoded using XML and must not contain DTD references or XML
processing instructions. Figure 8-4 illustrates the detailed schema for SOAP messages using the notation introduced in Figure 6-5. If a header is present in the message, it must be the first
immediate child of the Envelope element. The Body element either directly follows the Header
element or must be the first immediate child of the Envelope element if no header is present.
Because the root element Envelope is uniquely identified by its namespace, it allows processing tools to immediately determine whether a given XML document is a SOAP message.
The main information the sender wants to transmit to the receiver should be in the body of the message. Any additional information needed for intermediate processing or added-value services
e.g., authentication, security, transaction control, or tracing and auditing goes into the header. This is the common approach for communication protocols. The header contains information that
SOAP envelope SOAP header
SOAP body body block
body block header block
header block
attachment block attachment block
Actual message content required
Processing instructions Context information
optional Identifies message as
a SOAP message required
Arbitrary content optional
Envelope
Envelope Body
Body Header
Header header blocks
body blocks attachment blocks
Envelope
Envelope Body
Body Header
Header header blocks
body blocks attachment blocks
Figure 8-3: Schematic representation of a SOAP message. Highlighted are the required elements.
Ivan Marsic • Rutgers University
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can be used by intermediate nodes along the SOAP message path. The payload or body is the actual message being conveyed. This is the reason why the header is optional.
Each of the SOAP elements Envelope, Header, or Body can include arbitrary number of any
elements. Recall that the any element enables us to extend the XML document with elements not specified by the schema. Its namespace is indicated as other, which implies
elements from any namespace that is not the namespace of the parent element, that is, soap- env
. An example SOAP message containing a SOAP header block and a SOAP body is given as:
Listing 8-1: Example of a SOAP message. 1
soap-env:Envelope
2 xmlns:soap-env=http:www.w3.org200305soap-envelope 3 xmlns:xsd=http:www.w3.org2001XMLSchema
4 xmlns:xsi=http:www.w3.org2001XMLSchema-instance 5
soap-env:Header
6 ac:alertcontrol xmlns:ac=http:example.orgalertcontrol 7
soap-env:mustUnderstand=1
8 ac:priorityhighac:priority 9 ac:expires2006-22-00T14:00:00-05:00ac:expires
10 ac:alertcontrol 11
soap-env:Header
12 soap-env:Body
13 a:notify xmlns:a=http:example.orgalert 14 a:note xsi:type=xsd:string
Global attributes:
Envelope
?
soap-env:
Envelope
soap-env:
Header
soap-env:
Body
?
other:
any Envelope
?
soap-env:
Envelope
soap-env:
Envelope
soap-env:
Header
soap-env:
Body
?
other:
any Header
soap-env:
Header
?
other:
any
other:
anyAttribute
?
Header
soap-env:
Header
?
other:
any
other:
anyAttribute
?
Body
soap-env:
Body
?
other:
any
other:
anyAttribute
?
Body
soap-env:
Body
?
other:
any
other:
anyAttribute
?
soap-env:
role
soap-env:
mustUnderstand
soap-env:
encodingStyle
soap-env:
relay
soap-env:
role
soap-env:
mustUnderstand
soap-env:
encodingStyle
soap-env:
relay Fault
soap-env:
Fault Code
Reason Node
Role Detail
? ?
?
Fault
soap-env:
Fault Code
Reason Node
Role Detail
? ?
?
Figure 8-4: The XML schema for SOAP messages. The graphical notation is given in Figure 6-5. SOAP version 1.2 schema definition available at:
http:www.w3.org200305soap-envelope
.
