Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language

1.4.1 RFC 2119 Keywords

The keywords “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119 [IETF RFC 2119].

1.4.2 RFC 3986 Namespaces

Namespace names of the general form:

• "http://example.org/..." and

• "http://example.com/..."

represent application or context-dependent URIs [IETF RFC 3986].

1.4.3 XML Schema anyURI

This specification uses the XML Schema type xs:anyURI (see [XML Schema: Datatypes]). It is defined so that xs:anyURI values are essentially IRIs (see [IETF RFC 3987]). The conversion from xs:anyURI values to an actual URI is via an escaping procedure defined by (see [XLink 1.0]), which is identical in most respects to IRI Section 3.1 (see [IETF RFC 3987]).

For interoperability, WSDL authors are advised to avoid the US-ASCII characters: "<", ">", '"', space, "{", "}", "|", "\", "^", and "`", which are allowed by the xs:anyURI type, but disallowed in IRIs.

1.4.4 Prefixes and Namespaces Used in This Specification

This specification uses predefined namespace prefixes throughout; they are given in the following list. Note that the choice of any namespace prefix is arbitrary and not semantically significant (see [XML Namespaces]).

1.4.5 Terms Used in This Specification

This section describes the terms and concepts introduced in Part 1 of the WSDL Version 2.0 specification (this document).

Actual Value

As in [XML Schema: Structures], the expression "actual value" is used to refer to the member of the value space of the simple type definition associated with an attribute information item which corresponds to its normalized value. This will often be a string, but may also be an integer, a boolean, an IRI-reference, etc.

Inlined Schema

An XML schema that is defined in the wsdl:types element information item of a WSDL 2.0 description. For example, an XML Schema defined in an xs:schema element information item 3.1.2 Inlining XML Schema.

1.4.6 XML Information Set Properties

This specification refers to properties in the XML Information Set [XML Information Set]. Such properties are denoted by square brackets, e.g. [children], [attributes].

1.4.7 WSDL 2.0 Component Model Properties

This specification defines and refers to properties in the WSDL 2.0 Component Model 2. Component Model. Such properties are denoted by curly brackets, e.g. {name}, {interfaces}.

This specification uses a consistent naming convention for component model properties that refer to components. If a property refers to a required or optional component, then the property name is the same as the component name. If a property refers to a set of components, then the property name is the pluralized form of the component name.

1.4.8 Z Notation

Z Notation [Z Notation Reference Manual] was used in the development of this specification. Z Notation is a formal specification language that is based on standard mathematical notation. The Z Notation for this specification has been verified using the Fuzz 2000 type-checker [Fuzz 2000].

Since Z Notation is not widely known, it is not included the normative version of this specification. However, it is included in a non-normative version which allows to dynamically hide and show the Z Notation. Browsers correctly display the mathematical Unicode characters, provided that the required fonts are installed. Mathematical fonts for Mozilla Firefox can be downloaded from the Mozilla Web site.

The Z Notation was used to improve the quality of the normative text that defines the Component Model, and to help ensure that the test suite covered all important rules implied by the Component Model. However, the Z Notation is non-normative, so any conflict between it and the normative text is an error in the Z Notation. Readers and implementers may nevertheless find the Z Notation useful in cases where the normative text is unclear.

There are two elements of Z Notation syntax that conflict with the notational conventions described in the preceding sections. In Z Notation, square brackets are used to introduce basic sets, e.g. [ID], which conflicts with the use of square brackets to denote XML Information Set properties 1.4.6 XML Information Set Properties. Also, in Z Notation, curly brackets are used to denote set display and set comprehension, e.g. {1, 2, 3}, which conflicts with the use of curly brackets to denote WSDL 2.0 Component Model properties 1.4.7 WSDL 2.0 Component Model Properties. However, the intended meaning of square and curly brackets should be clear from their context and this minor notational conflict should not cause any confusion.

1.4.9 BNF Pseudo-Schemas

Pseudo-schemas are provided for each component, before the description of the component. They use BNF-style conventions for attributes and elements: "?" denotes optionality (i.e. zero or one occurrences), "*" denotes zero or more occurrences, "+" one or more occurrences, "[" and "]" are used to form groups, and "|" represents choice. Attributes are conventionally assigned a value which corresponds to their type, as defined in the normative schema. Elements with simple content are conventionally assigned a value which corresponds to the type of their content, as defined in the normative schema. Pseudo schemas do not include extension points for brevity.

<!-- sample pseudo-schema -->
<defined_element
      required_attribute_of_type_string="xs:string"
      optional_attribute_of_type_int="xs:int"? >
  <required_element />
  <optional_element />?
  <one_or_more_of_these_elements />+
  [ <choice_1 /> | <choice_2 /> ]*
</defined_element>

1.4.10 Assertions

Assertions about WSDL 2.0 documents and components that are not enforced by the normative XML schema for WSDL 2.0 are marked by a dagger symbol (†) at the end of a sentence. Each assertion has been assigned a unique identifier that consists of a descriptive textual prefix and a unique numeric suffix. The numeric suffixes are assigned sequentially and never reused so there may be gaps in the sequence. The assertion identifiers MAY be used by implementations of this specification for any purpose, e.g. error reporting.

The assertions and their identifiers are summarized in section E. Assertion Summary.

2.1.1 The Description Component

At a high level, the Description component is just a container for two categories of components: WSDL 2.0 components and type system components.

WSDL 2.0 components are interfaces, bindings and services. Type system components are element declarations and type definitions.

Type system components describe the constraints on a message's content. By default, these constraints are expressed in terms of the [XML Information Set], i.e. they define the [local name], [namespace name], [children] and [attributes] properties of an element information item. Type systems based upon other data models are generally accommodated by extensions to WSDL 2.0; see 6. Language Extensibility. In the case where they define information equivalent to that of a XML Schema global element declaration, they can be treated as if they were such a declaration.

This specification does not define the behavior of a WSDL 2.0 document that uses multiple schema languages for describing type system components simultaneously.

An Element Declaration component defines the name and content model of an element information item such as that defined by an XML Schema global element declaration. It has a {name} property that is the QName of the element information item and a {system} property that is the namespace IRI of the extension element information items for the type system, e.g. the namespace of XML Schema.

A Type Definition component defines the content model of an element information item such as that defined by an XML Schema global type definition. It has a {name} property that is the QName of the type and a {system} property that is the namespace IRI of the extension element information items for the type system, e.g. the namespace of XML Schema.

Interface, Binding, Service, Element Declaration, and Type Definition components are directly contained in the Description component and are referred to as top-level components. The top-level WSDL 2.0 components contain other components, e.g. Interface Operation and Endpoint, which are referred to as nested components. Nested components may contain other nested components. The component that contains a nested component is referred to as the parent of the nested component. Nested components have a {parent} property that is a reference to their parent component.

The properties of the Description component are as follows:

• {interfaces} OPTIONAL. A set of Interface components.

• {bindings} OPTIONAL. A set of Binding components.

• {services} OPTIONAL. A set of Service components.

• {element declarations} OPTIONAL. A set of Element Declaration components.

• {type definitions} REQUIRED. A set of Type Definition components.

The set of top-level components contained in the Description component associated with an initial WSDL 2.0 document consists of the components defined in the initial document, plus the components associated with the WSDL 2.0 documents that the initial document includes, plus the components defined by other WSDL 2.0 documents in the namespaces that the initial document imports. The component model makes no distinction between the components that are defined in the initial document versus those that are defined in the included documents or imported namespaces. However, any WSDL 2.0 document that contains component definitions that refer by QName to WSDL 2.0 components that belong to a different namespace MUST contain a wsdl:import element information item for that namespace (see 4.2 Importing Descriptions ). Furthermore, all QName references, whether to the same or to different namespaces must resolve to components (see 2.17 QName resolution ).

When using the XML Schema language to describe type system components, the inclusion of Element Declaration components and Type Definition components in a Description component is governed by the rules in 3.1 Using W3C XML Schema Definition Language.

In addition to WSDL 2.0 components and type system components, additional extension components MAY be added via extensibility 6. Language Extensibility. Further, additional properties to WSDL 2.0 and type system components MAY also be added via extensibility.

2.1.2 XML Representation of Description Component

<description
      targetNamespace="xs:anyURI" >
  <documentation />*
  [ <import /> | <include /> ]*
  <types />?
  [ <interface /> | <binding /> | <service /> ]*
</description>

WSDL 2.0 descriptions are represented in XML by one or more WSDL 2.0 Information Sets (Infosets), that is one or more description element information items. A WSDL 2.0 Infoset contains representations for a collection of WSDL 2.0 components that share a common target namespace and zero or more wsdl:import element information items 4.2 Importing Descriptions that correspond to a collection with components from multiple target namespaces.

The components directly defined or included within a Description component are said to belong to the same target namespace. The target namespace therefore groups a set of related component definitions and represents an unambiguous name for the intended semantics of the collection of components. The value of the targetNamespace attribute information item SHOULD be dereferencable.^† It SHOULD resolve to a human or machine processable document that directly or indirectly defines the intended semantics of those components.^† It MAY resolve to a WSDL 2.0 document that provides service description information for that namespace.^†

If a WSDL 2.0 document is split into multiple WSDL 2.0 documents (which may be combined as needed via 4.1 Including Descriptions), then the targetNamespace attribute information item SHOULD resolve to a master WSDL 2.0 document that includes all the WSDL 2.0 documents needed for that service description.^† This approach enables the WSDL 2.0 component designator fragment identifiers to be properly resolved.

Components that belong to imported namespaces have different target namespace values than that of the importing WSDL 2.0 document. Thus importing is the mechanism to use components from one namespace in the definition of components from another namespace.

Note that each WSDL 2.0 document or type system component of the same kind must be uniquely identified by its qualified name. That is, if two distinct components of the same kind (Interface, Binding, etc.) are in the same target namespace, then their QNames MUST be unique. However, different kinds of components (e.g., an Interface component and a Binding component) MAY have the same QName. Thus, QNames of components must be unique within the space of those components in a given target namespace.

The description element information item has the following Infoset properties:

• A [local name] of description.

• A [namespace name] of "http://www.w3.org/ns/wsdl".

• One or more attribute information items amongst its [attributes] as follows:

  • A REQUIRED targetNamespace attribute information item as described below in 2.1.2.1 targetNamespace attribute information item.

  • Zero or more namespace qualified attribute information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

• Zero or more element information items amongst its [children], in order as follows:^†

  1. Zero or more documentation element information items (see 5. Documentation).

  2. Zero or more element information items from among the following, in any order:

     • Zero or more include element information items (see 4.1 Including Descriptions)

     • Zero or more import element information items (see 4.2 Importing Descriptions)

     • Zero or more namespace-qualified element information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

  3. An OPTIONAL types element information item (see 3. Types).

  4. Zero or more element information items from among the following, in any order:

     • interface element information items (see 2.2.2 XML Representation of Interface Component).

     • binding element information items (see 2.7.2 XML Representation of Binding Component).

     • service element information items (see 2.12.2 XML Representation of Service Component).

     • Zero or more namespace-qualified element information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

2.1.3 Mapping Description's XML Representation to Component Properties

The mapping from the XML Representation of the description element information item (see 2.1.2 XML Representation of Description Component) to the properties of the Description component is described in Table 2-1.

2.2.1 The Interface Component

An Interface component describes sequences of messages that a service sends and/or receives. It does this by grouping related messages into operations. An operation is a sequence of input and output messages, and an interface is a set of operations.

An interface can optionally extend one or more other interfaces. To avoid circular definitions, an interface MUST NOT appear in the set of interfaces it extends, either directly or indirectly. ^† The set of operations available in an interface includes all the operations defined by the interfaces it extends directly or indirectly, together with any operations it directly defines. The operations directly defined on an interface are referred to as the declared operations of the interface. In the process, operation components that are equivalent per 2.15 Equivalence of Components are treated as one single component. The interface extension mechanism behaves in a similar way for all other components that can be defined inside an interface, namely Interface Fault components.

Interfaces are named constructs and can be referred to by QName (see 2.17 QName resolution). For instance, Binding components refer to interfaces in this way.

The properties of the Interface component are as follows:

• {name} REQUIRED. An xs:QName.

• {extended interfaces} OPTIONAL. A set of declared Interface components which this interface extends.

• {interface faults} OPTIONAL. The set of declared Interface Fault components. Note that the namespace name of the {name} property of each Interface Fault in this set is the same as the namespace name of the {name} property of this Interface component.

• {interface operations} OPTIONAL. A set of declared Interface Operation components. Note that the namespace name of the {name} property of each Interface Operation in this set is the same as the namespace name of the {name} property of this Interface component.

For each Interface component in the {interfaces} property of a Description component, the {name} property MUST be unique.^†

2.2.2 XML Representation of Interface Component

<description>
  <interface
        name="xs:NCName" 
        extends="list of xs:QName"?
        styleDefault="list of xs:anyURI"? >
    <documentation />*
    [ <fault /> | <operation /> ]*
  </interface>
</description>

The XML representation for an Interface component is an element information item with the following Infoset properties:

• A [local name] of interface

• A [namespace name] of "http://www.w3.org/ns/wsdl"

• One or more attribute information items amongst its [attributes] as follows:

  • A REQUIRED name attribute information item as described below in 2.2.2.1 name attribute information item with interface [owner element].

  • An OPTIONAL extends attribute information item as described below in 2.2.2.2 extends attribute information item.

  • An OPTIONAL styleDefault attribute information item as described below in 2.2.2.3 styleDefault attribute information item.

  • Zero or more namespace qualified attribute information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

• Zero or more element information items amongst its [children], in order, as follows:

  1. Zero or more documentation element information items (see 5. Documentation).

  2. Zero or more element information items from among the following, in any order:

     • Zero or more fault element information items 2.3.2 XML Representation of Interface Fault Component.

     • Zero or more operation element information items 2.4.2 XML Representation of Interface Operation Component.

     • Zero or more namespace-qualified element information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

2.2.3 Mapping Interface's XML Representation to Component Properties

The mapping from the XML Representation of the interface element information item (see 2.2.2 XML Representation of Interface Component) to the properties of the Interface component is as described in Table 2-2.

Recall that, per 2.2.1 The Interface Component, the Interface components in the {extended interfaces} property of a given Interface component MUST NOT contain that Interface component in any of their {extended interfaces} properties, that is to say, recursive extension of interfaces is disallowed.

2.3.1 The Interface Fault Component

A fault is an event that occurs during the execution of a message exchange that disrupts the normal flow of messages.

A fault is typically raised when a party is unable to communicate an error condition inside the normal message flow, or a party wishes to terminate a message exchange. A fault message may be used to communicate out of band information such as the reason for the error, the origin of the fault, as well as other informal diagnostics such as a program stack trace.

An Interface Fault component describes a fault that MAY occur during invocation of an operation of the interface. The Interface Fault component declares an abstract fault by naming it and indicating the contents of the fault message. When and how the fault message flows is indicated by the Interface Operation component.

The Interface Fault component provides a clear mechanism to name and describe the set of faults an interface may generate. This allows operations to easily identify the individual faults they may generate by name. This mechanism allows the ready identification of the same fault occurring across multiple operations and referenced in multiple bindings as well as reducing duplication of description for an individual fault.

Faults other than the ones described in the Interface component may also be generated at run-time, i.e. faults are an open set. The Interface component describes faults that have application level semantics, i.e. that the client or service is expected to handle, and potentially recover from, as part of the application processing logic. For example, an Interface component that accepts a credit card number may describe faults that indicate the credit card number is invalid, has been reported stolen, or has expired. The Interface component does not describe general system faults such as network failures, out of memory conditions, out of disk space conditions, invalid message formats, etc., although these faults may be generated as part of the message exchange. Such general system faults can reasonably be expected to occur in any message exchange and explicitly describing them in an Interface component is therefore uninformative.

The properties of the Interface Fault component are as follows:

• {name} REQUIRED. An xs:QName.

• {message content model} REQUIRED. An xs:token with one of the values #any, #none, #other, or #element.^† A value of #any indicates that the fault content is any single element. A value of #none indicates there is no fault content. A value of #other indicates that the fault content is described by some other extension property that references a declaration in a non-XML extension type system. A value of #element indicates that the fault consists of a single element described by the global element declaration referenced by the {element declaration} property. This property is used only when the fault is described using an XML-based data model.

• {element declaration} OPTIONAL. A reference to an Element Declaration component in the {element declarations} property of the Description component. This element represents the content or “payload” of the fault. When the {message content model} property has the value #any or #none the {element declaration} property MUST be empty.^†

• {parent} REQUIRED. The Interface component that contains this component in its {interface faults} property.

For each Interface Fault component in the {interface faults} property of an Interface component, the {name} property must be unique. Note that this constraint is enforced by the normative WSDL 2.0 XML schema.

Interface Fault components are uniquely identified by the QName of the enclosing Interface component and QName of the Interface Fault component itself.

In cases where, due to an interface extending one or more other interfaces, two or more Interface Fault components have the same value for their {name} property, then the component models of those Interface Fault components MUST be equivalent (see 2.15 Equivalence of Components). ^† If the Interface Fault components are equivalent then they are considered to collapse into a single component. Within the same Interface component, if two Interface Fault components are not equivalent then their {name} properties MUST NOT be equal.

Note that, due to the above rules, if two interfaces that have the same value for the namespace name of their {name} property also have one or more faults that have the same value for their {name} property, then those two interfaces cannot both form part of the derivation chain of a derived interface unless those faults are the same fault.

For the above reason, it is considered good practice to ensure, where necessary, that the local name of the {name} property of Interface Fault components within a namespace SHOULD be unique, thus allowing such derivation to occur without inadvertent error.^†

If a type system NOT based on the XML Infoset [XML Information Set] is in use (as considered in 3.2 Using Other Schema Languages) then additional properties would need to be added to the Interface Fault component (along with extension attributes to its XML representation) to allow associating such message types with the message reference.

2.3.2 XML Representation of Interface Fault Component

<description>
  <interface>
    <fault
          name="xs:NCName" 
          element="union of xs:QName, xs:token"? >
      <documentation />*
    </fault>
  </interface>
</description>

The XML representation for an Interface Fault component is an element information item with the following Infoset properties:

• A [local name] of fault

• A [namespace name] of "http://www.w3.org/ns/wsdl"

• One or more attribute information items amongst its [attributes] as follows:

  • A REQUIRED name attribute information item as described below in 2.3.2.1 name attribute information item with fault [owner element].

  • An OPTIONAL element attribute information item as described below in 2.3.2.2 element attribute information item with fault [owner element].

  • Zero or more namespace qualified attribute information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

• Zero or more element information item amongst its [children], in order, as follows:

  1. Zero or more documentation element information items (see 5. Documentation).

  2. Zero or more namespace-qualified element information item s whose [namespace name] is NOT " http://www.w3.org/ns/wsdl " .

2.3.3 Mapping Interface Fault's XML Representation to Component Properties

The mapping from the XML Representation of the fault element information item (see 2.3.2 XML Representation of Interface Fault Component) to the properties of the Interface Fault component is as described in Table 2-3.

2.4.1 The Interface Operation Component

An Interface Operation component describes an operation that a given interface supports. An operation is an interaction with the service consisting of a set of (ordinary and fault) messages exchanged between the service and the other parties involved in the interaction. The sequencing and cardinality of the messages involved in a particular interaction is governed by the message exchange pattern used by the operation (see {message exchange pattern} property).

A message exchange pattern defines placeholders for messages, the participants in the pattern (i.e., the sources and sinks of the messages), and the cardinality and sequencing of messages exchanged by the participants. The message placeholders are associated with specific message types by the operation that uses the pattern by means of message and fault references (see {interface message references} and {interface fault references} properties). The service whose operation is using the pattern becomes one of the participants of the pattern. This specification does not define a machine understandable language for defining message exchange patterns, nor does it define any specific patterns. The companion specification, [WSDL 2.0 Adjuncts] defines a set of such patterns and defines identifying IRIs any of which MAY be used as the value of the {message exchange pattern} property.

The properties of the Interface Operation component are as follows:

• {name} REQUIRED. An xs:QName.

• {message exchange pattern} REQUIRED. An xs:anyURI identifying the message exchange pattern used by the operation. This xs:anyURI MUST be an absolute IRI (see [IETF RFC 3987]).^†

• {interface message references} OPTIONAL. A set of Interface Message Reference components for the ordinary messages the operation accepts or sends.

• {interface fault references} OPTIONAL. A set of Interface Fault Reference components for the fault messages the operation accepts or sends.

• {style} OPTIONAL. A set of xs:anyURIs identifying the rules that were used to construct the {element declaration} properties of {interface message references}. (See 2.4.1.2 Operation Style.) These xs:anyURIs MUST be absolute IRIs (see [IETF RFC 3986]).^†

• {parent} REQUIRED. The Interface component that contains this component in its {interface operations} property.

For each Interface Operation component in the {interface operations} property of an Interface component, the {name} property MUST be unique. Note that this constraint is enforced by the normative WSDL 2.0 XML schema.

Interface Operation components are uniquely identified by the QName of the enclosing Interface component and QName of the Interface Operation component itself.

In cases where, due to an interface extending one or more other interfaces, two or more Interface Operation components have the same value for their {name} property, then the component models of those Interface Operation components MUST be equivalent (see 2.15 Equivalence of Components).^† If the Interface Operation components are equivalent then they are considered to collapse into a single component. Within the same Interface component, if two Interface Operation components are not equivalent then their {name} properties MUST NOT be equal.

Note that, due to the above rules, if two interfaces that have the same value for the namespace name of their {name} property also have one or more operations that have the same value for their {name} property, then those two interfaces cannot both form part of the derivation chain of a derived interface unless those operations are the same operation.

For the above reason, it is considered good practice to ensure, where necessary, that the {name} property of Interface Operation components within a namespace SHOULD be unique, thus allowing such derivation to occur without inadvertent error.^†

More than one Interface Fault Reference component in the {interface fault references} property of an Interface Operation component may refer to the same message label. In that case, the listed fault types define alternative fault messages. This allows one to indicate that there is more than one type of fault that is related to that message.

2.4.2 XML Representation of Interface Operation Component

<description>
  <interface>
    <operation
          name="xs:NCName" 
          pattern="xs:anyURI"?
          style="list of xs:anyURI"? >
      <documentation />*
      [ <input /> | <output /> | <infault /> | <outfault /> ]*
    </operation>
  </interface>
</description>

The XML representation for an Interface Operation component is an element information item with the following Infoset properties:

• A [local name] of operation

• A [namespace name] of "http://www.w3.org/ns/wsdl"

• Two or more attribute information items amongst its [attributes] as follows:

  • A REQUIRED name attribute information item as described below in 2.4.2.1 name attribute information item with operation [owner element].

  • An OPTIONAL pattern attribute information item as described below in 2.4.2.2 pattern attribute information item with operation [owner element].

  • An OPTIONAL style attribute information item as described below in 2.4.2.3 style attribute information item with operation [owner element].

  • Zero or more namespace qualified attribute information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

• One or more element information item amongst its [children], in order, as follows:

  1. Zero or more documentation element information items (see 5. Documentation).

  2. One or more element information items from among the following, in any order:

     • One or more element information items from among the following, in any order:

       • Zero or more input element information items (see 2.5.2 XML Representation of Interface Message Reference Component).

       • Zero or more output element information items (see 2.5.2 XML Representation of Interface Message Reference Component).

       • Zero or more infault element information items (see 2.6.2 XML Representation of Interface Fault Reference).

       • Zero or more outfault element information items (see 2.6.2 XML Representation of Interface Fault Reference).

     • Zero or more namespace-qualified element information items whose [namespace name] is NOT "http://www.w3.org/ns/wsdl".

2.4.3 Mapping Interface Operation's XML Representation to Component Properties

The mapping from the XML Representation of the operation element information item (see 2.4.2 XML Representation of Interface Operation Component) to the properties of the Interface Operation component (see 2.4.1 The Interface Operation Component) is as described in Table 2-4.

2.5.1 The Interface Message Reference Component

An Interface Message Reference component defines the content, or payload, of a message exchanged in an operation. By default, the message content is defined by an XML-based type system such as XML Schema. Other type systems may be used via the WSDL 2.0 type system extension mechanism.

A message exchange pattern defines a set of placeholder messages that participate in the pattern and assigns them unique message labels within the pattern (e.g. 'In', 'Out'). The purpose of an Interface Message Reference component is to associate an actual message element (XML element declaration or some other declaration (see 3.2 Using Other Schema Languages)) with a message in the pattern, as identified by its message label. Later, when the message exchange pattern is instantiated, messages corresponding to that particular label will follow the element assignment made by the Interface Message Reference component.

The properties of the Interface Message Reference component are as follows:

• {message label} REQUIRED. An xs:NCName. This property identifies the role this message plays in the {message exchange pattern} of the Interface Operation component this message is contained within.