Question

Consider the relational schema given below, where eId of the relation dependent is a foreign

key referring to empId of the relation employee. Assume that every employee has at least one

associated dependent in the dependent relation.

Employee (empId, empName, empAge)

Dependent(depId, eId, depName, depAge)

Consider the following relational algebra query:

Π_empId(employee)-Π_empId (employee⋈(empId = eID)∧(empAge ≤ depAge)dependent)

The above query evaluates to the set of empIds of employees whose age is greater than that of
1. some dependent.
2. all dependents
3. some of his/her dependents
4. all of his/her dependents

Answer 1

Correct Answer - Option 4 : all of his/her dependents

Explanation:

Example:

Employee Relation:

EmpID	empName	empAge
e1	A	20
e2	B	25
e3	C	24

 

Dependent Relation:

depID	eID	depName	Age
d1	e1	X	30
d2	e1	Y	25
d3	e1	Z	20
d4	e2	P	18
d5	e2	P	17
d7	e3	Z	35

 

R1=Π_empId (employee⋈(empId = eID)∧(empAge ≤ depAge)dependent)

Output : e1,e3

R2=Π_empId(employee)

Output: e1,e2,e3

R = R2 - R1= {e1,e2,e3} - {e1,e3} = e2

• e2 is output that is saying that set of empIds of employees whose age is greater than that of all of his/her dependents.