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The <message> element describes the data being exchanged between the web service providers and the consumers.

• Each Web Service has two messages: input and output.
• The input describes the parameters for the web service and the output describes the return data from the web service.
• Each message contains zero or more <part> parameters, one for each parameter of the web service function.
• Each <part> parameter associates with a concrete type defined in the <types> container element.

Let us take a piece of code from the WSDL Example chapter −

<message name = "SayHelloRequest">
   <part name = "firstName" type = "xsd:string"/>
</message>

<message name = "SayHelloResponse">
   <part name = "greeting" type = "xsd:string"/>
</message>

Here, two message elements are defined. The first represents a request message SayHelloRequest, and the second represents a response message SayHelloResponse.

Each of these messages contains a single part element. For the request, the part specifies the function parameters; in this case, we specify a single firstName parameter. For the response, the part specifies the function return values; in this case, we specify a single greeting return value.