• Description:
  • An XML grammar for describing network services as collections of communication endpoints capable of exchanging messages
• History:
  • Originally designed by IBM, Microsoft, and Ariba
  • Later submitted to the World Wide Web Consortium (W3C) for standardization

WSDL uses the XSD type system, for example:

  <complexType name="Book">
     <!-- Either the following group must occur or else the
          href attribute must appear, but not both. -->
     <sequence minOccurs="0" maxOccurs="1">
         <element name="title" type="xsd:string"/>
         <element name="firstauthor" type="Person"/>
         <element name="secondauthor" type="Person"/>
     </sequence>
     <attribute name="href" type="uriReference"/>
     <attribute name="id" type="ID"/>
  </complexType>
  

• Components:
  • Messages consist of one or more logical parts
  • Each part is associated with a type
• Reason for Messages:
  • Each method has exactly one input and one output
  • So each message element has one or more part elements, each of which represents what would be called a parameter in a language like Java

An Example

  <message name="requestFlights"> 
    <part name="time"   type="xsd:dateTime"/> 
    <part name="origin" type="xsd:string"/> 
    <part name="dest"   type="xsd:string"/> 
  </message> 
  <message name="requestFlightsResponse"> 
    <part name="result" type="xsd:ArrayOfString"/> 
  </message> 
  

• Defined:
  • A named set of abstract operations and the abstract messages involved
  • Essentially, a Java interface
• Attributes and Elements:
  • Contain operation elements
  • The name attribute provides a unique name among all port types defined within in the enclosing WSDL document

• Attributes:
  • name
  • parameterOrder (optional)
• Elements:
  • input (optional)
  • output (optional)
• Classification of Operations:
  • One-way (i.e., the endpoint receives a message)
  • Request-response (i.e., the endpoint first receives a message and then sends a correlated message)
  • Solicit-response (i.e., the endpoint first sends a message and then receives a correlated message)
  • Notification (i.e., the endpoint sends a message)

An Example

  <portType name="TicketAgent"> 
    <operation name="listFlights" parameterOrder="time origin dest"> 
      <input message="requestFlights" name="requestFlights"/> 
      <output message="requestFlightsResponse" name="requestFlightsResponse"/> 
    </operation> 
  </portType>        
  

• An Observation:
  • A portType element, like an interface in Java, cannot be instantiated
• Bindings Defined:
  • Provides the information needed to "realize" a portType
  • "Defines message format and protocol details for operations and messages defined by a particular portType"
• Common Bindings:
  • HTTP
  • SOAP over HTTP
  • SOAP over SMTP

An Example

  <wsdl:binding name="TicketAgencyBinding" type="TicketAgent">
    <soap:binding style="document"
                  transport="http://schemas/xmlsoap.org/soap/http"/>
    <wsdl:operation name="listFlights">
      <wsdl:input>
        <soap:body use="literal" />
      </wsdl:input>
      <wsdl:output>
        <soap:body use="literal" />
      </wsdl:output>
    </wsdl:operation>
  </wsdl:binding>
  

• Defined:
  • A port elements defines an individual endpoint by specifying a single address for a binding
• An Example:

  •   <port binding="TicketAgentBinding" name="TicketAgentPort">
        <soap:address location="http://www.ticketdog.com/soap/">
      </port>
      

• Defined:
  • A service element groups a set of related port elements together
• Ports within a Service:
  • None of the ports communicate with each other (e.g. the output of one port is not the input of another)
  • If a service has several ports that share a port type, but employ different bindings or addresses, the ports are alternatives