When creating a service, component, or reference for a SY composite in SY Visual Editor, you will first select the contract interface. However, if a WSDL file imports another WSDL file as follows:

stockquoteservice.wsdl (<wsdl:binding>, <wsdl:service>)
    -> stockquote.wsdl (<wsdl:types>, <wsdl:message>, <wsdl:portType>)

then both stockquoteservice.wsdl and stockquote.wsdl will show up in Select WSDL file and portType wizard but you can choose only the latter stockquote.wsdl (OK button is disabled for the former stockquoteservice.wsdl).

This appears to be because SY tooling cannot recognise wsdl:import in stockquoteservice.wsdl.