please answer #4

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? [3] 2. 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). [4] 3. What is the minimum possible number of attributes of a key for an entity set E? Then what is the maximum? [4] 4. We think of relationships in the ER model as having keys, just as entity sets do. Let R be a relationship betweer entity sets E1 and E2, where K1 and K2 are the set of attributes that is a key for entity set E1 and E2, respectively. What is the minimum possible number of attributes of a key for R (in terms of K1 and K2 ) under the assumption that: a. R is many-many [2]; b. R is many-one from E1 to E2 [2]; c. R is many-one from E2 to E1[2]; d. R is one-one [2]