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WebSphere Application Server - IBM Redbooks

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SOAP has the following characteristics:<br />

► SOAP is designed to be simple and extensible.<br />

► All SOAP messages are encoded using XML.<br />

► SOAP is transport protocol independent. HTTP is one of the supported<br />

transports, hence, SOAP can be run over existing Internet infrastructure.<br />

► There is no distributed garbage collection. Therefore, call by reference is not<br />

supported by SOAP; a SOAP client does not hold any stateful references to<br />

remote objects.<br />

► SOAP is operating system independent and not tied to any programming<br />

language or component technology. It is object model neutral.<br />

Due to these characteristics, it does not matter what technology is used to<br />

implement the client, as long as the client can issue XML messages. Similarly,<br />

the service can be implemented in any language, as long as it can process XML<br />

messages.<br />

Overview<br />

Historically, SOAP was meant to be a network and transport neutral protocol to<br />

carry XML messages. SOAP over HTTP became the premier way of<br />

implementing this protocol, to the point that the latest SOAP specification<br />

mandates HTTP support.<br />

However, conceptually there is no limit to the network protocol that can be<br />

utilized. For example, because HTTP is a transport that does not guarantee<br />

delivery and is non-transactional, SOAP messages can also be transferred by a<br />

messaging software such as MQSeries.<br />

SOAP remote procedure call (RPC) is the latest stage in the evolution of SOAP;<br />

the body of a SOAP message contains a call to a remote procedure (expressed<br />

in XML) and the parameters to pass in (again, expressed in XML).<br />

The SOAP standard specifies three aspects of XML-based message exchange.<br />

Overall message format<br />

A SOAP message is an envelope containing zero or more headers and exactly<br />

one body. The envelope is the top element of the XML document, providing a<br />

container for control information, the addressee of a message, and the message<br />

itself.<br />

Headers transport any control information such as quality of service attributes.<br />

The body contains the message identification and its parameters.<br />

Chapter 11. Working with Web services 361

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