Does SOAP have IDL

From reading the spec I don't see that SOAP has IDL (CORBA speak here).
Isn't it kind of a problem that a programmer has to know what the signature
of a function is.  With the Apache SOAP system the parameters are loaded
into and array.  Is there anyway defined to use perhaps XML Schema as a form
of IDL.  Does just loading parameters into an array represent the consensus
or am I missing something?

Matthew Jones
mjones@netsilicon.com