Top down SOAP Web services include creating WSDL document to create a contract between the web service and the client, with a required code as an option. This is also known as Contract-first approach. The top-down approach is difficult to implement because classes must be written to confirm the contract defined in WSDL. One of the benefits of this method is that both client and server code can be written in parallel.
Bottom up SOAP web services require the code to be written first and then WSDL is generated. It is also known as Contract-last approach. Since WSDL is created based on the code, bottom-up approach is easy to implement and client codes must wait for WSDL from the server side to start working.
