XML Schema provides enables you to describe complex types as compositions of simple types. This is the key to being able to support objects; if you can describe an object's data with mappings from the implementation language to SOAP types you can describe the object in an XML payload. Note that you cannot describe business logic (behavioral semantics) or complex relationships (such as inheritance) with XML Schema. The likelihood of that happening anytime soon seems pretty close to zero.

• XML Schema simple types
• Custom types defined with XML Schema

Among the responsibilities of a SOAP implementation is mapping the types as they are represented in the Envelope to primitives and objects that the implementing language understands.