Web Services Description Language:
WSDL is defined as WSDL is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. The operations and messages are described abstractly, and then bound to a concrete network protocol and message format to define an endpoint. Related concrete endpoints are combined into abstract endpoints (services).
WSDL is having five parts..
1. WSDL definition
Typically code is a XML document having definition at the root and type ,Message,PortType,Binding as child elements.
<types> tag defines data types used by the web service in XML Schema.Even the schema can be defined as a child element of <types>. This can be imported from external URL
<Message> tag defines the representation of all messages. More over that is abstruct in nature.
<PortType> tag is also an abstruct represenatation of the operations. It also depicts the message exchange patterns. This is represented as public methods used by a program. All input,output parameters are represented as a message.
<binding> tag connects web service interfaces into a physical transport protocol.
WSDL follows SOAP processing nodes with the following message exchange pattern(MEP)
1. Request response(Service consumer transmits a message to service provider,Provider should respond to the request.)
2. Fire and forget(Service consumer transmits a message to service provider but does not expect a response from service provider.like ping service )