The Web service client developer is essentially the user of the Web service, the person who develops a client application to use a Web service based on the definition provided by a WSDL file they obtain from a Web service deployer. The client developer ensures that the Web service they choose for their application uses a SOAP message format supported by their own Web service client technology. They also ensure that they have the necessary documentation (often supplied by the Web service deployer) that explains the client programming model required by the Web service they are using.