Consider a real time scenario. An E-Commerce website. Suppose you have Entered SONY and PENDRIVE as the keyword in querybox. The company SONY has many products as well as many companies are manufacturing pendrives. So when we are requesting a query in application level, it goes to logical level and after fetching the information(consider COMPANY and Product are two entities with more than one relationships) it returns us the result. Suppose there is a maintainance is going on and we are on the view or application level, we are not facing any problems. When we are placing a order that is stored in their database(which is also a change in logical level) but it is not affecting us(user). Hope my answer has justified the question. If I am wrong please clarify me.