Which web service provides detailed contracts through a WSDL file?

The correct choice is linked to the characteristics of SOAP (Simple Object Access Protocol). SOAP is a protocol specifically designed for exchanging structured information in the implementation of web services. One of its key features is the use of WSDL (Web Services Description Language) files, which provide a detailed contract regarding the service.

WSDL files outline the available functions of a web service, including the parameters and types of data it accepts, the responses it sends, and the protocols used for communication. This standardized approach allows developers to understand how to interact with the web service without needing to rely on additional documentation.

In contrast, other web service types like REST (Representational State Transfer) do not utilize WSDL; they are more flexible and often use JSON or XML for communication without a formal contract like WSDL. GraphQL also operates fundamentally differently by allowing clients to request only the data they need, and XML-RPC is a simpler remote procedure call protocol that does not provide the comprehensive, structured service contract that SOAP does with its WSDL files.