Thanks for the suggestion of XML::Compile::WSDL11 that I was not aware.
But now I managed to fix the code generated and I can successfully interact with HP Service Management. This code is relatively small, and the user-level is actually minimal. But Obviously I will have to fix the generator.
I will anyway look at the other alternative
but at first my question was not xml/xsd attributes related, but perl syntax attributes related. And I still do not know where the notation used by SOAP::WSDL is coming.