WS-MessageDelivery Version 1.0

1.1 Example

Consider a request-response operation description in a WSDL 1.1 document. Typically, when used with SOAP over HTTP, the same HTTP connection is used to send the request and response messages and request/response correlation is implicit. This implicit approach does not work well for asynchronous responses or when the message goes through multiple hops or when the request and response message use different transports. The example SOAP messages show how AMDP can be used in the request and response messages to implement the request-response operation without relying on transport specific features.

Request Message:

<soap11:Envelope
    xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery"
    xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"
    xmlns:soapbind="http://schemas.xmlsoap.org/wsdl/soap/">
<soap11:Header xmlns:myns="http://example.com/wsdl">

<wsmd:MessageOriginator>
    <wsmd:uri>http://example.org/client-A </wsmd:uri>
</wsmd:MessageOriginator>

<wsmd:MessageDestination 
    wsmd:wsdlLocation="http://example.com/wsdl http://example.com/wsdl/app.wsdl"
    wsmd:targetNamespace="http://example.com/wsdl">
    <wsdl11:service name="myservice" wsmd:portType="myns:myPortType">
        <wsdl11:port name="myport" binding="myns:myBinding">
            <soapbind:address location="http://example.com/wsdl/impl"/>
        </wsdl11:port>
    </wsdl11:service>
</wsmd:MessageDestination>

<wsmd:ReplyDestination>
    <wsmd:uri>http://example.org/client-A/replyDestination</wsmd:uri>
</wsmd:ReplyDestination>

<wsmd:FaultDestination>
    <wsmd:uri>http://example.org/client-A/faultDestination</wsmd:uri>
</wsmd:FaultDestination>

<wsmd:MessageID>
    uuid:58f202ac-22cf-11d1-b12d-002035b29092
</wsmd:MessageID>

<wsmd:OperationName>myRequestResponseOperation</wsmd:OperationName>

...
</soap11:Header>
<soap11:Body>
...
</soap11:Body>
</soap11:Envelope>

There are six SOAP header blocks in the request message:

1. wsmd:MessageOriginator - This header block specifies the identity of the client invoking the Web service.

2. wsmd:MessageDestination - This header block identifies the service element in the WSDL document that described the service to which the request message is being sent.

3. wsmd:ReplyDestination - This header block identifies the dereferenceable URI that is used by the Web service to send the response message.

4. wsmd:FaultDestination - This header block identifies the dereferenceable URI that is used by the Web service to send a fault back.

5. wsmd:MessageID - This header block assigns a unique URI to the message and is used to identify the message. The unique URI in this header is used for correlating the response message with the request message.

6. wsmd:OperationName - This header block identifies the name of the operation that designates the specific message exchange.

Response Message:

<soap11:Envelope
     xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/"
     xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery"
     xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"
     xmlns:soapbind="http://schemas.xmlsoap.org/wsdl/soap/">
<soap11:Header xmlns:myns="http://example.com/wsdl">

<wsmd:MessageOriginator
   wsmd:wsdlLocation="http://example.com/wsdl http://example.com/wsdl/app.wsdl"
   wsmd:targetNamespace="http://example.com/wsdl">
   <wsdl11:service name="myservice" wsmd:portType="myns:myPortType">
      <wsdl11:port name="myport" binding="myns:myBinding">
         <soapbind:address location="http://example.com/wsdl/impl"/>
      </wsdl11:port>
   </wsdl11:service>
</wsmd:MessageOriginator>

<wsmd:MessageDestination>
   <wsmd:uri>http://example.com/Client-A/replyDestination</wsmd:uri>
</wsmd:MessageDestination>

<wsmd:MessageID>
   uuid:5a389ad2-22dd-11d1-aa77-002035b29092
</wsmd:MessageID>

<wsmd:MessageReference 
   wsmd:reason="http://www.w3.org/2004/04/ws-messagedelivery/reason/response">
   uuid:58f202ac-22cf-11d1-b12d-002035b29092
</wsmd:MessageReference>

<wsmd:OperationName>myRequestResponseOperation</wsmd:OperationName>

...
</soap11:Header>
<soap11:Body>...
</soap11:Body>
</soap11:Envelope>

There are five SOAP header blocks in the response message:

1. wsmd:MessageOriginator - This header block specifies the service that sent the response message. This value is used to determine the sender of the response message.

2. wsmd:MessageDestination - This header block identifies the sender of the initial request.

3. wsmd:MessageID - This header block assigns a unique URI to the message and is used to identify the message.

4. wsmd:MessageReference - This header block identifies the request message to which this response is being sent. The attribute wsmd:reason specifies that the message being sent is a response in a request-response operation. This header is used to correlate the response message with the request message at the initial sender.

5. wsmd:OperationName - This header block identifies the name of the operation that designates the specific message exchange.

The advantage of using the SOAP header blocks is that, all the information is in the SOAP message and is transport independent. For example, myns:myBinding could use an asynchronous transport that does not provide direct support for correlating request and response SOAP messages (unlike HTTP). This would allow the implementation to use such an asynchronous transport binding to implement the request-response operation.

1.2 Notational Conventions

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].

This specification uses a number of namespace prefixes throughout; they are listed in Table 1. Note that the choice of any namespace prefix is arbitrary and not semantically significant [XML Information Set].

1.3 Conformance

This specification describes AMDP, mapping of AMDP to SOAP, use of AMDP in MEPs, description of WS-MessageDelivery feature in WSDL, WSRefs and the Callback pattern. This specification does not mandate a particular implementation, but all the "MUST" and "MUST NOT" must be correctly implemented by an implementation that claims conformance to this specification. Typically, whether a Web service adheres to this specification or not is expressed in the WSDL document that describes the Web service through the use of extensibility points and features, as described in this specification.

An implementation is not required to implement all the mandatory aspects of this specification. For example, an implementation that does not implement the Callback pattern does not have to implement the requirements specified for Callback.

1.4 Relation to Other Specifications

This specification is designed to work in conjunction with existing XML technologies, including but not limited to SOAP 1.1/1.2 and WSDL 1.1. WS-MessageDelivery can be used as a building block for other technologies. For example, other specifications can use WSRefs in message payloads to implement complex services. This specification can be used to implement MEPs defined in WSDL 1.1; especially for message that require end-to-end semantics and for asynchronous transports.

The ideas in this specification could also be used with the current Working Group Draft of WSDL 2.0 [WSDL 2.0 Part 1] and the MEPs defined therein [WSDL 2.0 Part 2]. Sections 6 Message Delivery and WSDL 2.0 and B Appendix: WSDL 2.0 and AMDPs provide an illustration of how this might occur.

2.1 WSRefs in WSDL 1.1

A WSDL 1.1 Web service reference is considered to be an element whose type is ultimately derived from wsdl11:tService, with the following restrictions:

• All wsdl11:port children element of the WSRef MUST implement the same wsdl11:portType. This wsdl11:portType may optionally be indicated as a value of the attribute 'wsmd:portType' as described below.

• Bindings for all wsdl11:port children elements must bind every wsdl11:part of the input or output wsdl11:message in the wsdl11:portType to the corresponding input or output protocol elements that are exchanged over the network. This restriction is very similar to R2209 of WS-I Basic Profile 1.0 [BP 1.0].

The restrictions listed above ensure that all the ports within a WSRef implement the same contract (i.e. the portType).

This definition of a WSRef provides an extensible, WSDL 1.1 centric, typed notion of a Web service reference. It also makes the wsdl11:service element a WSRef (when the restrictions listed above are also met). Using XML Schema derivation by restriction, it is possible to declare a WSRef and fix the portType, binding or both. Examples of such WSRefs with fixed portType/binding are listed in section 2.1.2 Examples.

A WSRef, similar to a service element in a WSDL description, may contain assertions about the capability of the service that it represents, such as QoS assertions. They are expected to be expressed using extensibility elements within the wsdl11:service element.

<wsdl11:definitions
     targetNamespace="http://example.com/wsdl11-example"
     xmlns:tns="http://example.com/wsdl11-example"
     xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery"
     xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/">
. . .
<wsdl11:service name="myservice" wsmd:portType="tns:myportType">
   <wsdl11:port name="myport" binding="tns:mybinding">
       <soapbind:address location="http://example.com/wsdl-example1/impl"/>
   </wsdl11:port>
</wsdl11:service>
</wsdl:definitions>

3.1 wsmd:destination type

The wsmd:destination designates a destination for messages. The destinations significant for message delivery are represented by wsmd:destination as shown by the following pseudo-schema syntax:

<... wsmd:targetNamespace="xs:anyURI"? 
     wsmd:wsdlLocation="list-of-xs:anyURI"? >
[<wsdl11:service> | <wsmd:uri> | <wsmd:serviceQName> | <extensibility_element>* ]</...>

A wsmd:destination type MUST contains one of the following

1. a URI or

2. a QName

3. a WSDL service element

It allows two optional attributes called wsmd:wsdlLocation and wsmd:targetNamespace . These attributes are defined below in detail.

When an element of type wsmd:destination contains a URI, this URI identifies the destination which is either not a Web service, or a web service that shares the binding and the message that is being specified by the WSDL definition. For example, a client invoking a request-response operation of a Web service would be represented by a URI since the client agrees to use the binding that is defined by the service.

The wsmd:destination may contain a WSDL 1.1 service element. In the case where wsmd:destination contains a service element, the destination designates a Web service. The service elements as noted above are WSRefs. This type can be used in conjunction with WSDL 1.1 descriptions.

The wsmd:destination may also contain a QName that corresponds to a service element defined in a WSDL document.

The wsmd:destination type is extensible, and hence may contain additional elements or attributes that are not defined using the wsmd target namespace. The properties MessageOriginator, MessageDestination, ReplyDestination, and FaultDestination are represented by using wsmd:destination schema type. See A Appendix: Schema for full description.

The attribute value wsmd:wsdlLocation is ignored when a destination is designated by a URI. The attribute value wsmd:targetNamespace is ignored when a destination is specified using a service QName or a URI.

3.2 MessageOriginator

The MessageOriginator property identifies the node that sent the message. MessageOriginator is defined by the following pseudo-schema:

<wsmd:MessageOriginator 
    wsmd:targetNamespace="xs:anyURI"?
    wsmd:wsdlLocation="list-of-xs:anyURI"? >
[<wsdl11:service> | <wsmd:uri> | <wsmd:serviceQName> | <extensibility_element>*]
</wsmd:MessageOriginator>

The MessageOriginator element information item has the following Infoset properties:

• A [local name] of MessageOriginator.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

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

  • An OPTIONAL wsmd:targetNamespace attribute information item as described above

  • An OPTIONAL wsmd:wsdlLocation attribute information item as described above.

  • Zero or more namespace qualified attribute information items. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

• One or more element information items as follows:

  • Either a service element information item as defined by WSDL 1.1, a uri element information item or a serviceQName element information item as defined above.

  • Zero or more namespace-qualified element information items amongst its [children]. The [namespace name] of such element information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the MessageOriginator element information item is wsmd:destination.

3.3 MessageDestination

MessageDestination identifies the destination or target of the message. MessageDestination is defined by the following pseudo-schema:

<wsmd:MessageDestination 
    wsmd:targetNamespace="xs:anyURI"?
    wsmd:wsdlLocation="list-of-xs:anyURI"? >
[<wsdl11:service> | <wsmd:uri> | <wsmd:serviceQName> | <extensibility_element>*]
</wsmd:MessageDestination>

The MessageDestination element information item has the following Infoset properties:

• A [local name] of MessageDestination.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

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

  • An OPTIONAL wsmd:targetNamespace attribute information item as described above

  • An OPTIONAL wsmd:wsdlLocation attribute information item as described above.

  • Zero or more namespace qualified attribute information items. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

• One or more element information items as follows:

  • Either a service element information item as defined by WSDL 1.1, a uri element information item or a serviceQName element information item as defined above.

  • Zero or more namespace-qualified element information items amongst its [children]. The [namespace name] of such element information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the MessageDestination element information item is wsmd:destination.

3.4 ReplyDestination

ReplyDestination identifies the destination to which a reply to the message may be sent. The value of this property, if present, MUST be used to send a reply when the binding used does not specify how and where the reply is sent. ReplyDestination is defined by the following pseudo-schema:

<wsmd:ReplyDestination 
    wsmd:targetNamespace="xs:anyURI"?
    wsmd:wsdlLocation="list-of-xs:anyURI"? >
[<wsdl11:service> | <wsmd:uri> | <wsmd:serviceQName> | <extensibility_element>*]
</wsmd:ReplyDestination>

The ReplyDestination element information item has the following Infoset properties:

• A [local name] of ReplyDestination.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

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

  • An OPTIONAL wsmd:targetNamespace attribute information item as described above

  • An OPTIONAL wsmd:wsdlLocation attribute information item as described above.

  • Zero or more namespace qualified attribute information items. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

• One or more element information items as follows:

  • Either a service element information item as defined by WSDL 1.1, a uri element information item or a serviceQName element information item as defined above.

  • Zero or more namespace-qualified element information items amongst its [children]. The [namespace name] of such element information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the ReplyDestination element information item is wsmd:destination.

3.5 FaultDestination

FaultDestination identifies the destination to which a fault may be sent. The value of this property, if present, MUST be used to send a fault back when the binding used does not specify how and where the reply is sent.

FaultDestination is defined by the following pseudo-schema:

<wsmd:FaultDestination 
    wsmd:targetNamespace="xs:anyURI"?
    wsmd:wsdlLocation="list-of-xs:anyURI"? >
[<wsdl11:service> | <wsmd:uri> | <wsmd:serviceQName> | <extensibility_element>*]
</wsmd:FaultDestination>

The FaultDestination element information item has the following Infoset properties:

• A [local name] of FaultDestination.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

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

  • An OPTIONAL wsmd:targetNamespace attribute information item as described above

  • An OPTIONAL wsmd:wsdlLocation attribute information item as described above.

  • Zero or more namespace qualified attribute information items. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

• One or more element information items as follows:

  • Either a service element information item as defined by WSDL 1.1, a uri element information item or a serviceQName element information item as defined above.

  • Zero or more namespace-qualified element information items amongst its [children]. The [namespace name] of such element information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the FaultDestination element information item is wsmd:destination.

3.6 MessageID

The value of the MessageID property must be unique and serves to uniquely identify a message.

The MessageID element information item has:

• A [local name] of MessageID.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the MessageID element information item is xs:anyURI.

3.7 MessageReference

MessageReference allows a message to be correlated to another message and specifies the reason for the correlation. The MessageReference property consists of two parts each of which is of type xs:anyURI. The first part consists of a MessageID, the ID of the message that triggered the generation of the message containing the MessageReference. The second optional part consists of the Reason for the message and is of type xs:anyURI.

MessageReference is defined by the following pseudo-schema:

<wsmd:MessageReference 
    wsmd:reason="xs:anyURI"? >xs:anyURI
</wsmd:MessageReference>

The MessageReference element information item has:

• A [local name] of MessageReference.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

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

  • An OPTIONAL reason attribute information item. The [local name] property of which is reason, [namespace name] property is "http://www.w3.org/2004/04/ws-messagedelivery" and the type is xs:anyURI.

  • Zero or more namespace qualified attribute information items. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the MessageReference element information item is wsmd:messageReference.

There are four predefined values for the wsmd:reason attribute:

1. "http://www.w3.org/2004/04/ws-messagedelivery/reason/response" -- implies that the message is a response and the ID of the message in the wsmd:MessageReference identifies the request message.

2. "http://www.w3.org/2004/04/ws-messagedelivery/reason/fault" - implies that the message is a fault and the ID of the message in the wsmd:MessageReference identifies the message that triggered this fault.

3. "http://www.w3.org/2004/04/ws-messagedelivery/reason/notification" -- implies that the message is a notification and the ID of the message in the wsmd:MessageReference identifies the message that requested the notification.

4. "http://www.w3.org/2004/04/ws-messagedelivery/reason/callback" -- implies that the message is a ultimate response message (the Callback message) and the ID of the message in the wsmd:MessageReference identifies the message initial request message.

If omitted, the implicit value for the reason attribute is "http://www.w3.org/2004/04/ws-messagedelivery/reason/response".

3.8 OperationName

The value of the OperationName property must be the NCName of the operation specified in WSDL that indicates the specific message exchange. The value of the property in conjunction with the WSRef of the web service that defines the service is used to infer the specific operation uniquely.

The OperationName element information item has:

• A [local name] of OperationName.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

The type of the OperationName element information item is xs:NCName.

3.9 Mapping of AMDP to SOAP

Each of the six abstract message delivery properties get mapped to a SOAP header block when using SOAP (version 1.1 or 1.2) as the protocol. The processing semantics defined by SOAP 1.1 or SOAP 1.2 apply when AMDP are sent as SOAP headers blocks.

For example:

<soap11:Envelope  
    xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"
    xmlns:soapbind="http://schemas.xmlsoap.org/wsdl/soap/"
    xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery">
<soap11:header xmlns:cr="http://example.com/creditbureau">

<wsmd:MessageOriginator>
   <wsmd:uri>http://example.com/app/myMsgOrg</wsmd:uri>
</wsmd:MessageOriginator>

<wsmd:MessageDestination
    wsmd:targetNamespace="http://example.com/creditbureau"
    wsmd:wsdlLocation="http://example.com/creditbureau/wsdl">
   <wsdl11:service name="CreditBureauService"
       wsmd:portType="cr:CreditBureauPT">
       <wsdl11:port binding="cr:SOAPCreditBureauBinding">
          <soapbind:address location="http://example.com/creditbureau/impl"/>
       </wsdl11:port>
   </wsdl11:service>
</wsmd:MessageDestination>

<wsmd:MessageID>http://example.com/myMsgId</wsmd:MessageID>

<wsmd:MessageReference>http://example.com/creditbureau/response-0123456789
</wsmd:MessageReference>

<wsmd:OperationName>generateCreditReport</wsmd:OperationName>

</soap11:header>
<soap11:body>
...
</soap11:body>
</soap11:Envelope>

4.1 Declaring the usage of AMDP in WSDL 1.1

In WSDL 1.1 documents, an extension element, wsmd:MessageDeliveryFeature is used to indicate that message delivery properties are in effect. This element is defined by using the pseudo-schema:

<wsmd:MessageDeliveryFeature/>

The extension element can be present as a child element of operation (which can be a child element of wsdl11:portType or wsdl11:binding), or a child element of wsdl11:binding. For example,

<wsdl11:definitions  
    xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"  
    xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery  
    targetNamespace="http://example.com/myNamespace"> 
  
    <wsdl11:binding name="myBinding">    . . .        
        <wsmd:MessageDeliveryFeature/>     
    </wsdl11:binding>
</wsdl11:definitions>

The MessageDeliveryFeature element information item has the following Infoset properties:

• A [local name] of MessageDeliveryFeature.

• A [namespace name] of "http://www.w3.org/2004/04/ws-messagedelivery".

• Zero or more namespace qualified attribute information items amongst its [attributes]. The [namespace name] of such attribute information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

• Zero or more namespace-qualified element information items amongst its [children]. The [namespace name] of such element information items MUST NOT be "http://www.w3.org/2004/04/ws-messagedelivery".

4.2 WSDL 1.1 Message Exchange Patterns and AMDP

WSDL 1.1 defines a basic set of four Message Exchange Patterns or operations. It is possible to define a composite MEP that is composed of predefined operations in WSDL 1.1. Such a composite MEP, when used in conjunction with AMDP, MUST NOT violate the AMDP rules defined for the predefined MEPs. For an example of such a composite MEP see 5 CallBack Pattern.

This section specifies the how AMDP are used in the context of the four operations that are defined in WSDL 1.1. For each message in an operation ('Input', 'Output' or 'Fault'), this section defines the mandatory properties, the optional properties and restrictions on the value of the properties. The optional properties MAY be used by a composite transmission primitive to implement the composite transmission primitive.

In every message the value of the property MessageOriginator is used to identify the sender of the message; the value of the property MessageDestination is used by the endpoint implementation to target the recipient of the message and the value of the property MessageID is used to uniquely identify the message.

5.1 Declaring Callbacks in WSDL Documents

In WSDL documents, an extension element, wsmd:ResponseOperation is used to indicate that the Callback pattern is being used. This extensibility element specifies the portType and the operation (and optionally binding) used for sending the ultimate response message.

For WSDL 1.1, the extensibility element can be present as a child element of wsdl11:operation (where the wsdl11:operation is either a child element of wsdl11:portType or wsdl11:binding) that describe the responding Web service.

For examples of use of this extensibility element see sections 5.2 Callback Representation Using Two Operations with Input Messages and 5.3 Callback Representation Using Two Operations with Input-Output Messages.

<wsmd:ResponseOperation 
    wsmd:interface="xs:QName" 
    wsmd:operation="xs:NCName"
    wsmd:binding="xs:QName"?/>

5.2 Callback Representation Using Two Operations with Input Messages

The example below illustrates the use of two operations with input messages to represent Callback.

<wsdl11:definitions
    xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery"
    xmlns:tns="http://example.com/callback/2-input"
    targetNamespace="http://example.com/callback/2-input">
. . .
<wsdl11:portType name="processRequestPortType">
    <wsdl11:operation name="processRequest">
         <wsdl11:input message="tns:requestMessage"/>
         <wsmd:ResponseOperation interface="tns:processResponsePortType"
                                  operation="processResponse"/>
         <wsmd:MessageDeliveryFeature/>
    </wsdl11:operation>
</wsdl11:portType>

<wsdl11:portType name="processResponsePortType">
     <wsdl11:operation name="processResponse">
          <wsdl11:input message="tns:responseMessage"/>...
          <wsmd:MessageDeliveryFeature/>
      </wsdl11:operation>
</wsdl11:portType>

<wsdl11:service name="CBService">
    <wsdl11:port name="CBPort">
        <soap11:address location="http://example.com/cb-impl1"/>
    </wsdl11:port>
</wsdl11:service>
</wsdl11:definitions>

In this example, there are two portTypes. The portType processRequestPortType (implemented by the responding Web service) contains the operation processRequest that is correlated to the operation processResponse in portType processResponsePortType (implemented by the requesting Web service). The extensibility element wsmd:ResponseOperation specifies the portType and the operation that is used by the requesting Web service. Web service CBService implements the operation processRequest. When this service is invoked, the AMDP SOAP headers provide the necessary information about the correlation id that is to be used in the ultimate response message and the destination (which will include the binding and endpoint information) where the ultimate response must be sent.

The figure below depicts the messages sent between the requesting Web service and the responding Web service when the Callback pattern is implemented using two operations with input messages.

To represent Callback using two input messages:

• The extensibility element wsmd:ResponseOperation MUST be present in the wsdl11:operation element. This operation is implemented by the responding Web service.

• The responding Web service and requesting Web service MUST implement the AMDP feature.

The initial request message sent to the responding Web service MUST have the value of the wsmd:MessageOriginator property set to represent the requesting Web service. The responding Web service uses the interface/operation/binding information provided by the wsmd:ResponseOperation extensibility element as well as the value of the wsmd:MessageOriginator property (which is only available at runtime) to invoke the requesting Web service and send the ultimate response message. It is an error if the value of the wsmd:MessageOriginator property of the initial request message does not support/implement the portType/operation/binding specified by the wsmd:ResponseOperation extensibility element in the WSDL description.

The initial request message MUST specify a value for the wsmd:MessageID property. This value is used as the correlation id and appears as the value of the wsmd:MessageReference property of the ultimate response message. The wsmd:reason attribute value of the ultimate response message is "http://www.w3.org/2004/04/ws-messagedelivery/reason/callback".

5.3 Callback Representation Using Two Operations with Input-Output Messages

The example below illustrates the use of two input-output operations to represent Callback.

<wsdl11:definitions
    xmlns:wsdl11="http://schemas.xmlsoap.org/wsdl/"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:wsmd="http://www.w3.org/2004/04/ws-messagedelivery"
    xmlns:tns="http://example.com/callback/2-input-output"
    targetNamespace="http://example.com/callback/2-input-output">
. . .
<wsdl11:portType name="processRequestPortType">
    <wsdl11:operation name="processRequest">
        <wsdl11:input message="tns:requestMessage"/>
        <wsdl11:output message="tns:requestMessageAck"/>
        <wsmd:ResponseOperation interface="tns:processResponsePortType"
                                operation="processResponse"/>
        <wsmd:MessageDeliveryFeature/>
    </wsdl11:operation>
</wsdl11:portType>

<wsdl11:portType name="processResponsePortType">
    <wsdl11:operation name="processResponse">
        <wsdl11:input message="tns:responseMessage"/>
        <wsdl11:output message="tns:responseMessageAck"/>
        <wsmd:MessageDeliveryFeature/>
    </wsdl11:operation>
</wsdl11:portType>

<wsdl11:service name="CBService">
    <wsdl11:port name="CBPort">
        <soap11:address location="http://example.com/cb-impl2"/>
    </wsdl11:port>
</wsdl11:service>
</wsdl11:definitions>

In this example, there are two portTypes. portType processRequestPortType (implemented by the responding Web service) contains the operation processRequest which is correlated to the operation processResponse in portType processResponsePortType (implemented by the requesting Web service). The extensibility element wsmd:ResponseOperation specifies the portType and the operation that is used by the requesting Web service. Web service CBService implements the operation processRequest. When this service is invoked, the AMDP SOAP headers provide the necessary information about the correlation id that is to be used in the ultimate response message and the destination (which will include the binding and endpoint information) where the ultimate response must be sent.

The figure below depicts the messages sent between the requesting Web service and the responding Web service when the Callback pattern is implemented using two operations with input messages.

To represent Callback using a pair of input-output messages:

• The extensibility element wsmd:ResponseOperation MUST be present in the wsdl11:operation element. This operation is implemented by the responding Web service.

• The responding Web service and requesting Web service MUST implement the AMDP feature.

The initial request message sent to the responding Web service MUST have the value of the wsmd:MessageOriginator property set to represent the requesting Web service. The responding Web service immediately sends a message back to the requesting Web service using the same binding -- this message is an acknowledgement of the receipt of the initial request and is not the Callback message. The responding Web service uses the portType/operation/binding information provided by the wsmd:ResponseOperation extensibility element as well as the value of the wsmd:MessageOriginator property (which is only available at runtime) to invoke the requesting Web service and send the ultimate response message. It is an error if the value of the wsmd:MessageOriginator property of the initial request message does not support/implement the interface/operation/binding specified by the wsmd:ResponseOperation extensibility element in the WSDL description. The requesting Web service then sends an acknowledgement of the Callback message to the responding Web service.

The initial request message MUST specify a value for the wsmd:MessageID property. This value is used as the correlation id and appears as the value of the wsmd:MessageReference property of the ultimate response message. The wsmd:reason attribute value of the ultimate response message is "http://www.w3.org/2004/04/ws-messagedelivery/reason/callback".

The initial request message MUST specify a value for the wsmd:FaultDestination property and the wsmd:ReplyDestination property. The wsmd:MessageOriginator property value of the initial request message identifies the ultimate response destination and not the fault or reply destination.