Introduction to Services

The term "Web services" can apply to a number of different ways to send information back and forth, but this guide focuses on the sending and receiving of SOAP messages. SOAP messages are XML documents that consist of an "envelope" containing a "payload":

Example SOAP Message:

<?xml version='1.0' ?>     <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"     xmlns:wsa="http://www.w3.org/2005/03/addressing">       <env:Header>               <wsa:MessageID>           http://ws.apache.org/9C21DE32-DB42-1228-C42E-66CB101421AD         </wsa:MessageID>         <wsa:ReplyTo>           <wsa:Address>http://example.com/projects/clientApp</wsa:Address>         </wsa:ReplyTo>              <wsa:To>http://example.com/axis2/publishingService</wsa:To>              <wsa:Action>http://example.com/axis2/addDocument</wsa:Action>           </env:Header>      <env:Body>             <addDocument>        <docTitle>What I Did On My Summer Vacation</doctitle>        <docSubtitle>Children's Essays from Accross the World</docSubtitle>        <docLocation>contentRepos/summerVac.doc</docLocation>       </addDocument>            </env:Body>     </env:Envelope>

This XML document consists of the outer element, or the SOAP Envelope, and its contents. The SOAP Envelope is in the SOAP namespace, http://www.w3.org/2003/05/soap-envelope, prefixed as env:, and contains up to two children. This envelope is a standard format that pertains to every single SOAP message sent and received by any SOAP Web service.

The contents of the Envelope consists of two parts, the first being the SOAP headers, the contents of the env:Header element. These headers, such as the WS-Addressing elements shown here, provide additional information about the message and how it should be handled. A SOAP message may carry headers relating to several aspects of the message, or it may carry no headers at all. These headers are typically processed by the message handlers.

The third and arguably most important part of the message is the payload, which consists of the contents of the env:Body element. This is the actual message intended for the receiver, and is the information that the main application will ultimately process.