WSDL 1.1 can define message parts. These parts can be present in both the input as well as output messages of an operation in the portType definition. The Tools project should determine whether these parameters are IN, INOUT or OUT parameters and construct HOLDER objects in the generated SEI.

Example:

<message name="myRequest">
<part name="p1" type="xs:double" />
<part name="p2" type="xs:double" />
</message>

<message name="myResponse">
<part name="p2" type="xs:double" />
<part name="p3" type="xs:string" />
<part name="p4" type="xs:integer" />
</message>

<portType name="myService">
<operation name="myOperation" parameterOrder="p1 p2 p3">
<input message="tns:myRequest" />
<output message="tns:myResponse" />
</operation>
</portType>

The tools should consider the parameterOrder in the operation element and take:
a) p1 as an IN parameter.
b) p2 as INOUT (present both in input as well as in output)
c) p3 as OUT (only present in output and not input)
d) p4 as a return parameter. (not present in the parameter order but present in the output message)

A similar exercise for WSDL 2.0 has to be researched with an example.