An interesting MEP

Martin Gudgin/Jeff Schlimmer

A data item service

• Consider a service the provides data items to consumers
  • Such data items expire over time
• Service provides a port type for requesting an updated item
  • Single operation
  • Input message, output message (MEP2)

Example

<wsdl:definitions xmlns:wsdl='http://www.w3.org/@@@@/@@/wsdl' 
                  targetNamespace='http://example.org/datasrv'
                  xmlns:tns='http://example.org/datasrv'
                  xmlns:xstns='http://example.org/types' >

 <wsdl:types>

  <xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' 
             xmlns:xstns='http://example.org/types' 
             targetNamespace='http://example.org/types' >

   <xs:element name='DataRequest' type='xstns:DataRequest' />

   <xs:complexType name='DataRequest' >
    <xs:sequence>
     <xs:element name='ItemName' type='xs:QName' />
    </xs:sequence>
   </xs:complexType>

   <xs:element name='DataItem' type='xstns:DataItem' />

   <xs:complexType name='DataItem' >
    <xs:sequence>
     <xs:element name='Name' type='xs:QName' />
     <xs:element name='Value' />
     <xs:element name='Expires' type='xs:timeInstant??' />
    </xs:sequence>
   </xs:complexType>

  </xs:schema>

 </wsdl:types>

 <wsdl:message name='DataRequest' >
  <wsdl:part element='xstns:DataRequest' />
 </wsdl:message>

 <wsdl:message name='DataItem' >
  <wsdl:part element='xstns:DataItem' />
 </wsdl:message>

 <wsdl:portType name='ProvideDataItems' >
  <wsdl:operation name'ItemRequest' 
                  mep='http://www.w3.org/@@@@/@@/MEP2' >
   <wsdl:input message='tns:DataRequest' />
   <wsdl:output message='tns:DataItem' />
  </wsdl:operation>
 </wsdl:portType>

</wsdl:definitions>

Consider an HTTP binding

• Binding the operation to HTTP gives us
  • Request-response
  • Single channel
  • Synchronous behaviour

Consider a multicast binding

• Binding to multicast
  • Input message arrives in unicast
  • Output message sent over broadcast
• Output message delivered to all clients

Observations

• From the server perspective the operation is an input followed by an output
  • This is true for both bindings
  • Server can support both bindings at the same time
• From the client perspective, things are somewhat different

Client view - HTTP

• Client sends output message
• Client receives input message

Client view - Multicast

• Client sends output message
• Client receives input message
• Client might also receive unsolicited input messages
  • Due to DataRequest to server from other client