WSDL and XML

Estimated study time: 12 minutes.

WSDL (Web Services Description Language) is an XML-based format used to describe exactly what a web service does, how to call it, and what kind of response to expect.

Why WSDL Matters

Before a client can talk to a SOAP web service, it needs to know: What operations are available? What parameters do they need? What will the response look like? A WSDL document answers all of that in a machine-readable way.

Core Parts of a WSDL Document

• types — the data types used by the service (usually defined with XSD).
• message — the individual pieces of data being exchanged.
• portType — the set of operations the service supports.
• binding — how those operations map to an actual protocol (like SOAP over HTTP).
• service — the actual network address (endpoint) where the service can be reached.

A Simplified Example

<definitions name="StudentService">
  <message name="GetStudentRequest">
    <part name="StudentID" type="xsd:int"/>
  </message>
  <message name="GetStudentResponse">
    <part name="Name" type="xsd:string"/>
  </message>
  <portType name="StudentPortType">
    <operation name="GetStudent">
      <input message="GetStudentRequest"/>
      <output message="GetStudentResponse"/>
    </operation>
  </portType>
</definitions>