title: Don't allow users to update a table on back date by changing their system date
body: <p>I was thinking about a project on distribution management.</p>
  
  <p>Suppose I have a central database that contains all the sales info of the products manufactured by my company. I populate this database with fresh data from the distributors on fixed regular intervals.</p>
  
  <p>There are other local databases installed on the systems of the distributors. There are certain interfaces made on Java EE Platform through which they access their respective local database. Every week the distributors have to sync their databases with ours. When a distributor syncs with the database, our sales records get updated.</p>
  
  <p>The distributor shouldn't show sales for a back date. But, suppose, a distributor does that by changing his system date to add a sales invoice of back date to his local database. Then he syncs his database with ours and that sale gets reflected in our database.</p>
  
  <p>How can I as a programmer prevent him from doing that (provided that the interface is made by me).</p>