Table of contents

Appendices

3.2 Using Other Schema Languages

Since it is unreasonable to expect that a single schema language can be used to describe all possible Message Reference, Fault and Property component contents and their constraints, WSDL allows alternate schema languages to be specified via extensibility elements. An extensibility element information item MAY appear under the types element information item to identify the schema language employed, and to locate the schema instance defining the grammar for Message Reference and Interface Fault components or the constraint for Property components. Depending upon the schema language used, an element information item MAY be defined to allow embedding, if and only if the schema language can be expressed in XML.

A specification of extension syntax for an alternative schema language MUST include the declaration of an element information item, intended to appear as a child of the wsdl:types element information item, which references, names, and locates the schema instance (an "import" element information item). The extension specification SHOULD, if necessary, define additional properties of [The Definitions Component] (and extensibility attributes) to hold the components of the referenced type system. It is expected that additional extensibility attributes for Message Reference, Interface Fault and Property components will also be defined, along with a mechanism for resolving the values of those attributes to a particular imported type system component.

See [Examples of Specifications of Extension Elements for Alternative Schema Language Support.] for examples of using other schema languages. These examples reuse the {element declarations} property of [The Definitions Component] and the element attribute information items of the wsdl:input, wsdl:output and wsdl:fault element information items.