Which among the following defines the rules for communication between two systems when using web services?

Rules for communication between different systems need to be defined, such as: How one system can request data from another system; which specific parameters are needed in the data request; what would be the structure of the data produced. Normally, data is exchanged in XML files, and the structure of the XML file is validated against an .xsd file; what error messages to display when a certain rule for communication is not observed, to make troubleshooting easier. All of these rules for communication are defined in a file called WSDL (Web Services Description Language), which has the extension wsdl.