SilverlightDS simplifies many of the mundane steps required to use web services. It takes care of establishing the HTTP connections to the web services, converting the data returned to strongly typed values and establishing relationships between the various web service calls.
The SilverlightDS utility also tracks the state of your data. Simply put, if your SilverlightDS is in the process of "Committing" data back to the web services, trying to process a “Fetch” will not be allowed until the "Commit" finishes.