Answer:
[1] = 10
[2] = The same natural joins with their super entity set
[3] = Is in 3NF if R is in BCNF
[4] = Neither "1" or "2"
[5] = When changes in R.A are made
Explanation:
[1] The number of super keys of a relation R(A, B, C, D) with keys {A} and {B, C} is 10. The super keys of the given relations are {A}; {A, B}; {A,C}; {A,D}; {A,B,C}; {A,B,D}; {A,C,D}; {A,B,C,D}; {B,C}; {B,C,D}.
[2] key is used to uniquely identify entity from entity set. So key for every entity is unique. Subentities can have different attributes. Also functional dependencies can be different but natural join with their super subsets will be same.
[3] For a relation R to be in BCNF it must be in 3NF but If a relation R is in 3NF it is not necessary that it will be in BCNF.
[4] The natural join of relations R and S is expressed by R ✕ S.
[5] If tuple constraint references an attribute R.A to S.B then every time a change is done in R.A the tuple constraint is checked.
