what is the difference between top down and bottom up...

Top down SOAP web services involves creating WSDL document to a build a contract between web service and client. You can then add the required code. This is also known as contract first approach. The top-down approach is hard to implement because classes need to be written to confirm the contract established in WSDL. One of the advantages of using this approach is that it allows both client and server code to be written in parallel.
Bottom up SOAP web services require the code to be written first and then WSDL is created. It is also known as contract the last approach. Since WSDL is generated based on the code, bottom-up approach is easy to implement. Client codes have to wait for WSDL from the server side to start the work.

what is the difference between top down and bottom up approach in SOAP web services?