That is, the input message will contain a single part only which is well defined in a schema.
RPC style web service和document style web service的不同之处：The significant difference is that the former
can't be validated with a schema while the latter can. Therefore, document style web service is becoming the
dominant style. According to an organization called "WS-I" (web services interoperability organization), you
should use document style web services only.