WSDL.

    Web Services Description Language is an XML format for describing Web services. WSDL enables one to separate the description of the abstract functionality offered by a service from concrete details of a service description such as "how" and "where" that functionality is offered.
    - Data type information for all message requests and message responses
    - Binding information about the transport protocol to be used
    - Interface information describing all publicly available functions
    - Address information for locating the specified service

Operation patterns supported by WSDL.      One way
          The service receives a message.
     Request - Response
          The service receives a message and sends a response.
     Solicit - Response
          The service sends a message and receives a response.
     Notification
          The service sends a message.