I may not understand the question, but does the SAML profile for XACML not do what you want? It defines SOAP formats for authzDecisionQuery entries and responses, which should be all you need for WSDL.
I built one of them around the Sun interpreter for DOD / DISA (its on forge.mil) and a much faster version (not yet redone) around a fully compiled implementation that directly converts XACML to Java code. The main goal is readability, not speed, but it is about ten times faster.
IMO XACML works, but is absolutely terrible, like a language for people to look at. I'm more interested in finding a situation-specific language to express XACML semantics so people can understand them. Java is superior to XACML for these hands, but Java is pretty awkward as a domain specific language. Perhaps Groovy?
PS: Attempto Controlled English (ACE). , , ACE ( ). , , NSA .