[flexcoders] Passing complextype parameter to webservice

[kellis5137]

Hi,
I'm new to Flex and hoping you all might be able to answer a question
I have had for a while. In ActionScript, I'm trying to pass a
parameter to a web service. I'm using the WebService class in the
following way:
...
authenticationService = new WebService();
authenticationService.loadWSDL("http://localhost:8080/alfresco/wsdl/authentication-service.wsdl";);
authenticationService.startSession("parameter"); // startSession being
the name of the operation.
...

Now, the parameter is a complextype:

         <element name="startSession">
            <complexType>
               <sequence>
                  <element name="username" type="xsd:string"/>
                  <element name="password" type="xsd:string"/>
               </sequence>
            </complexType>
         </element>

How do I represent this type in ActionScript? As an object? I hope
this makes sense?! Thank you in advance for any help!
Keith