Structure of a Web-Services Description Language (WSDL) Document

Structure of a WSDL document:

Service

– Port definition

   – soap:address

Binding

– soap:binding

– operation

   – soap:operation

      – input

          – soap:body

      – output

          – soap:body

PortType

– operation

   – input

   – output

Message

– part

Types

Figure 1: WSDL Structure – visual representation of various sections of a WSDL and the relationships between them.

Any WSDL document is a combination of an abstract service interface and its concrete implementation.

The PortType section represents the service in an abstract way, similar to an ‘interface’ in object-oriented programming (OOP). In other words, it lays down the ‘contract’ between the service provider and the consumer by listing the various operations supported by the web-service as well as the required input and the resulting output of each operation. The inputs and outputs are listed as messages which are described in the Message section of the WSDL.

The Binding section is similar to an interface implementation in OOP. The ‘type’ attribute in the Binding tag points to the PortType  name which is being implemented.

The thing to keep in mind is that the Binding section is where the abstract web-service contract is implemented or realised. Thus, among other things the Binding section describes operational level details such as which protocol to use for transporting SOAP packets (usually HTTP) and how the web-service will be called (style and encoding).

The Service section describes one or more concrete ‘endpoints’ where the functionality of the service can be found.

Figure 1 shows these various sections of the WSDL and how they connect with each other.

Finally the Types section contains schema information for the various inputs and outputs from the web-service operations.