Transformation of Relational Expressions

Question 1
Marks : +2 | -2
Pass Ratio : 100%
If no rule can be derived from any combination of others then the set of rules is said to be ________
Primitive
Axiomatic
Minimal
Atomic
Explanation:
A set of equivalence rules is said to be minimal if no rule can be derived from any combination of others. Query optimizers use minimal sets of equivalence rules.
Question 2
Marks : +2 | -2
Pass Ratio : 100%
State true or false: The projection operation does not distribute over the union operation
True
False
Explanation:
The projection operation distributes over the union operation.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
Theta join operations are
Commutative
Associative
Distributive under projection
All of the mentioned
Explanation:
The theta join operations are commutative, associative and are distributive under projection.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
Which of the following set operations does the selection operation distribute over?
Union
Intersection
Difference
All of the mentioned
Explanation:
The selection operation distributes over Set union, intersection, set difference.
Question 5
Marks : +2 | -2
Pass Ratio : 100%
If on every legal database instant, the two expressions generate the same set of tuples, the expressions are called as
Equal
Equivalent
Similar
Identical
Explanation:
If on every legal database instant, the two expressions generate the same set of tuples, the expressions are called as Equivalent relational algebra expressions. The order of the tuples is completely irrelevant for equivalency.
Question 6
Marks : +2 | -2
Pass Ratio : 100%
Which of the following set operations is not commutative?
Union
Intersection
Set difference
None of the mentioned
Explanation:
The set difference operation is not commutative. As the position of the set difference operator affects the result of the operation.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
State true or false: Selection operations are commutative
True
False
Explanation:
Selection operations are commutative i.e. selection1(selection2(R)) = selection2(selection1(R)).
Question 8
Marks : +2 | -2
Pass Ratio : 100%
Which of the following operations are associative
Natural joins
Theta joins
Both the mentioned
None of the mentioned
Explanation:
Both natural join operation and theta join operation are associative. The commutativity and associativity of the join operations are important for join reordering in query optimization.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
State true or false: Multiple equivalence rules can be used one after the other on a query
True
False
Explanation:
Multiple equivalence rules can be used one after the other on a query or on parts of the query. This can be used to simplify the query greatly thus reducing its time complexity.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
Which of the following operations is associative
Set union
Set intersection
Set difference
Theta join
Explanation:
The theta join operation is associative within a certain set of conditions whereas the rest of the operations are non-associative in each and every condition.