Explain in detail about the Web services description language(WSDL).
The Web services description language (WSDL) is an XML-based language to describe services as a collection of accessible operations through messages. It defines interfaces and service interaction mechanisms, binding protocols, and network service details. It presents additional descriptions such as context, quality of service, and service-to-service relationship. By using its methods, it is possible to describe an object in a transparent, implementation-independent way.
The usage of WSDL also allows a basic service description in two parts as shown in Fig. 1.12.
This basic definition is separated in both service interface and implementation, allowing these parts to be reused separately.
(i) Service Interface Description Layer –
A service interface contains a WSDL service definition. This definition allows an interface can be used, instantiated, and referenced by multiple service implementation definitions.
A binding directive describes the protocol, data format, security, and other attributes of a particular service interface.
port type tag informs the Web service operation elements.
message tag is used to define data input and output regarding an operation.
type tag defines the complex data types inside a message.
An interface file describes the Web service, including the methods that are invoked, parameters that are sent and codification that is being utilized.
(ii) Service Implementation Description Layer –
It is a WSDL document that describes how a service interface is implemented by a service provider. A WEB-based service is modeled as a WSDL element which contains a WSDL – port elements collection (associated port and service searching) with a WSDL-binding interface-definition element.
An implementation file describes where the Web service is installed and how it could be accessed.
Likewise the interface and implementation definitions, the WSDL specifies extensions for protocol bindings and message formats, such as SOAP HTTP GET/POST and MIME.
