The Relational Model and Normalization Questions and Answers

Q: Given the functional dependency R → (S,T) , then it is also true that R → S.

Correct answer: TrueIf R determines the pair (S, T), then given a value of R the value of S is fixed - the pair could not be determined otherwise. This is the decomposition rule of Armstrong’s axioms, and it is what allows a dependency on a set of attributes to be broken down into a dependency on each of them separately. The converse does not follow.

Q: A candidate key is a determinant that determines all the other columns is a relation.

Correct answer: TrueA candidate key is a minimal set of attributes that uniquely identifies a row, and identifying the row fixes the value of every attribute in it - so the key functionally determines every other column. This is why candidate keys are determinants; the point of Boyce-Codd Normal Form is to insist that every determinant be one of them.

Q: The only reason for the existence of relations is to store instances of functional dependencies.

Correct answer: TrueA relation exists to record which values go with which, and every such association is a functional dependency - the key determines the non-key attributes. Seen that way, storing instances of functional dependencies is what a relation does, and a relation that stores dependencies belonging to more than one theme is exactly the one that suffers modification anomalies.

Q: A relation is in 5NF when multivalued dependencies are isolated in their own relation.

Correct answer: FalseIsolating multivalued dependencies in their own relations gives fourth normal form, not fifth. Fifth normal form, sometimes called project-join normal form, deals with join dependencies: relations that cannot be reconstructed correctly from any two of their projections but can from three or more.

Q: The functional dependency R → S means that the value of S can be determined when we are given a value of R.

Correct answer: TrueThis is the definition. R → S asserts that each value of R is associated with exactly one value of S, so knowing R is enough to determine S. R is the determinant, S the dependent attribute. It is a statement about the meaning of the data, so no set of sample rows can prove it - a single counterexample refutes it.

Q: Normalization reduces data redundancy but generally increases the number of joins needed to answer a query.

Correct answer: TrueSplitting data across more, narrower relations removes duplication and the update anomalies that come with it, but reassembling the information then requires joins. This trade-off is why analytical systems often denormalise deliberately.

Q: A relation can have more than one primary key.

Correct answer: FalseA relation may have several candidate keys, but exactly one of them is designated the primary key and the rest become alternate keys. What can involve several columns is a composite primary key, which is still a single key.

Q: A column that forms part of a foreign key can never contain a NULL value.

Correct answer: FalseReferential integrity requires only that a non-null foreign key match an existing primary key value. A NULL is permitted and simply means the relationship is unknown or does not apply, unless the column is separately declared NOT NULL.

Q: Every relation that is in BCNF is necessarily also in third normal form.

Correct answer: TrueThe normal forms are nested: BCNF is strictly stronger than 3NF, so satisfying it implies satisfying 3NF. The converse does not hold, since a 3NF relation with overlapping candidate keys can still violate BCNF.

Q: In a relation, the columns are sometimes called "attributes."

Correct answer: TrueColumns are attributes in the relational vocabulary, fields in the older file-processing one. Each attribute draws its values from a single domain, and attributes are identified by name rather than by position, which is why the order in which the columns are written does not matter.

71.

Given the functional dependency R → (S,T) , then it is also true that R → S.

A.True
B.False

Answer: A

Correct answer: True

If R determines the pair (S, T), then given a value of R the value of S is fixed - the pair could not be determined otherwise. This is the decomposition rule of Armstrong’s axioms, and it is what allows a dependency on a set of attributes to be broken down into a dependency on each of them separately. The converse does not follow.

Discuss in Forum

72.

A candidate key is a determinant that determines all the other columns is a relation.

A.True
B.False

Answer: A

Correct answer: True

A candidate key is a minimal set of attributes that uniquely identifies a row, and identifying the row fixes the value of every attribute in it - so the key functionally determines every other column. This is why candidate keys are determinants; the point of Boyce-Codd Normal Form is to insist that every determinant be one of them.

Discuss in Forum

73.

The only reason for the existence of relations is to store instances of functional dependencies.

A.True
B.False

Answer: A

Correct answer: True

A relation exists to record which values go with which, and every such association is a functional dependency - the key determines the non-key attributes. Seen that way, storing instances of functional dependencies is what a relation does, and a relation that stores dependencies belonging to more than one theme is exactly the one that suffers modification anomalies.

Discuss in Forum

74.

A relation is in 5NF when multivalued dependencies are isolated in their own relation.

A.True
B.False

Answer: B

Correct answer: False

Isolating multivalued dependencies in their own relations gives fourth normal form, not fifth. Fifth normal form, sometimes called project-join normal form, deals with join dependencies: relations that cannot be reconstructed correctly from any two of their projections but can from three or more.

Discuss in Forum

75.

The functional dependency R → S means that the value of S can be determined when we are given a value of R.

A.True
B.False

Answer: A

Correct answer: True

This is the definition. R → S asserts that each value of R is associated with exactly one value of S, so knowing R is enough to determine S. R is the determinant, S the dependent attribute. It is a statement about the meaning of the data, so no set of sample rows can prove it - a single counterexample refutes it.

Discuss in Forum

76.

Normalization reduces data redundancy but generally increases the number of joins needed to answer a query.

A.True
B.False

Answer: A

Correct answer: True

Splitting data across more, narrower relations removes duplication and the update anomalies that come with it, but reassembling the information then requires joins. This trade-off is why analytical systems often denormalise deliberately.

Discuss in Forum

77.

A relation can have more than one primary key.

A.True
B.False

Answer: A

Correct answer: False

A relation may have several candidate keys, but exactly one of them is designated the primary key and the rest become alternate keys. What can involve several columns is a composite primary key, which is still a single key.

Discuss in Forum

78.

A column that forms part of a foreign key can never contain a NULL value.

A.True
B.False

Answer: B

Correct answer: False

Referential integrity requires only that a non-null foreign key match an existing primary key value. A NULL is permitted and simply means the relationship is unknown or does not apply, unless the column is separately declared NOT NULL.

Discuss in Forum

79.

Every relation that is in BCNF is necessarily also in third normal form.

A.True
B.False

Answer: A

Correct answer: True

The normal forms are nested: BCNF is strictly stronger than 3NF, so satisfying it implies satisfying 3NF. The converse does not hold, since a 3NF relation with overlapping candidate keys can still violate BCNF.

Discuss in Forum

80.

In a relation, the columns are sometimes called "attributes."

A.True
B.False

Answer: A

Correct answer: True

Columns are attributes in the relational vocabulary, fields in the older file-processing one. Each attribute draws its values from a single domain, and attributes are identified by name rather than by position, which is why the order in which the columns are written does not matter.

Discuss in Forum

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