For very simple services that exchange only simple datatypes such as int or string, no special datatypes are generated. Usually, though, a service needs to exchange more complex data. In the Web service model, this data is exchanged as an XML document defined through an XML Schema and carried in a SOAP message. Other types of services can also use schema-defined XML to exchange complex data, although they are not required to.

When HydraExpress needs to process an XML Schema either contained or referenced in a WSDL file, the code generator acts as a schema compiler, creating a C++ data binding for the XML datatypes defined in the schema. This binding lets you use native C++ code to marshal, unmarshal, and manipulate the data carried by the XML datatypes. For a complete description of this binding mechanism, see the HydraExpress XML Binding Development Guide.