Most updates are updates (Posts, Puts or Deletes) to rows, processed per logic as shown in the example above. Sometimes, however, transactions require arguments. Consider giving an employee a raise, supplying the percent raise as a argument.
You can issue a POST like this:
https://MyServer/sample/v1/sample%3Aemployees/charlie?arg.RaisePercent=10
Which is handled by your logic like this, by reference to the Request Object: