1. describe the concept of physical data independence and its importance in database systems
2. List four significant differences between a file-processing system and a DBMS.
3. Describe the differences in meaning between the terms relation and relation schema.
4. List two reasons why null values might be introduced into the database.
5. Show that (proof), in SQL, <>all is identical to not in.
6. Show how to define a view total_credits(year, num_credits), giving the total number of credits taken by students in each year.