Messages are the abstract definition of the data being exchanged between the proxy and the Web Service. The first message element from SAS Web Service WSDL is shown in Fig 4 below.  

- <message name="GetFlightStatusSoapIn">

            <part name="parameters" element="s0:GetFlightStatus" />

  </message>

Fig 4: First message element from SAS Web Service WSDL document.

As we can see, the message element contains one or more logical parts. Parts are a flexible way of describing the logical abstract content of a message or to put it simply, a part may represent a parameter in a message. 

In our example from fig4, we can see the element “part” contains an element type “GetFlightStatus” from namespace “s0”, which in turn points to the same document with the definition (some times the same document can be referred to as “tns”): xmlns:s0="http://tempuri.org/" targetNamespace=http://tempuri.org/. The relationship between message and types is shown below in Fig 5:

Fig 5: Relationship between “message” and “types”

So from the above relationship we can derive: The message with name “GetFlightStatusSoapIn” contains a part called “parameters” of type “GetFlightStatus” element which is nothing but a sequence of two integers: namely “nFlightNo” and “nDayOffset”. There could be messages that contain parts with simple types like “string”. In that case the part may point to element types from the XSD namespace as shown in Fig 6 below. 

- <message name="GetFlightStatusHttpGetIn">

            <part name="nFlightNo" type="s:string" />

            <part name="nDayOffset" type="s:string" />

  </message>

Fig 6: message with simple types defined as parts.

Finally there could be many messages present in a service definition. In our example there are six different messages defined: a set of two messages (Request and Response), for the protocols “SOAP”, “HTTPGET” and “HTTP-POST”.