Why WSDL file?

We already know that WSDL is an XML standard document, is used to describe a web service. This description is required so that the client applications are able to understand what the web service  actually does.

WSDL describes: 

• How to call a web service (Using SOAP or HTTP protocol) 
• All the available operations which are exposed by the web service and their input and output structures. 
• Location of the web service or we can say the end point of the web service (Location where the service is running)

The WSDL file itself can look very complex to any user but it contain all the necessary information that any client application would require to use the relevant web service.

Why WSDL File?

The WSDL file is written in plain XML. So that the file can be read  by any programming language. But now with the WSDL file which is an XML , which can be understand by any programming language, we can now easily have a Java class consume the .NET , SAP, Python web service and vice versa. Hence the amount of coding effort is greatly reduced.