What is the usage of WSDL in a web service?

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WSDL is used in web service to describe the availability of service.

The correct answer would be:

WSDL (Web Services Description Language) in a web service is used to describe the functionalities provided by the service, including the operations that can be performed, the input and output parameters for each operation, and the communication protocols and message formats supported by the service. It acts as a contract between the service provider and consumer, enabling interoperability by allowing different systems to understand how to interact with the web service.