1What is logical data independence and why is it important?

2.Explain the di?erence between external, internal, and conceptual sche-mas. How are these di?erent schema layers related to the concepts of logical and physical data independence?

3.Scrooge McNugget wants to store information (names, addresses, de-scriptions of embarrassing moments, etc.) about the many ducks on his payroll. Not surprisingly, the volume of data compels him to buy a database system. To save money, he wants to buy one with the fewest possible features, and he plans to run it as a stand-alone application on his PC clone. Of course, Scrooge does not plan to share his list with anyone. Indicate which of the following DBMS features Scrooge should pay for; in each case, also indicate why Scrooge should (or should not) pay for that feature in the system he buys. 

1. A security facility. 

2. Concurrency control. 

3. Crash recovery. 

4. A view mechanism. 

5. A query language.

4.Describe the structure of a DBMS. If your operating system is upgraded to support some new functions on OS ?les (e.g., the ability to force some sequence of bytes to disk), which layer(s) of the DBMS would you have to rewrite to take advantage of these new functions?