Problem 6 [35] Please answer each of the questions in brief: 1. Why should we start modeling a real-world Database application with ER diagrams instead of going directly to a relational model? [5] 2. What are referential integrity constraints? Why are they important from both the data quality aspect, as well as the technical (programming) aspect? [10] 3. What are weak entity sets? Give an example where weak entity sets would be necessary (not the examples given in class think of your own). [10] 4. What is the minimum possible number of attributes of a key for an entity set E? Then what is the maximum? [2] 5. We think of relationships in the ER model as having keys, just as entity sets do. Let R be a relationship between entity sets Ej and E2, where K and Ky are the set of attributes that is a key for entity set Ej and E2, respectively. What is the minimum possible number of attributes of a key for R (in terms of K and K) under the assumption that: a. Ris many-many [2]; b. R is many-one from Eto E2 [2]; c. R is many-one from E2 to E1 [2]; d. R is one-one [2]