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 relation has cells that hold multi-value entries.

Correct answer: FalseOne of the defining conditions of a relation is that each cell contains a single value. A cell holding several values - a list of phone numbers, say - means the table is not in first normal form and is not a relation at all. The remedy is to move the repeating values into a separate relation.

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: Relations are categorized into normal forms according to the referential integrity constraints that they have.

Correct answer: FalseNormal forms are defined by the functional and multivalued dependencies a relation permits, not by referential integrity constraints. Referential integrity is a constraint between relations, requiring foreign key values to exist in the referenced relation, and it is entirely independent of how far a relation has been normalised.

Q: Keys made up of two or more attributes are called composite keys.

Correct answer: TrueA composite key is simply a key made up of more than one attribute, used where no single attribute is unique on its own - a line item identified by order number together with line number, for instance. It is still a key in every respect and must still be minimal, so that no constituent attribute could be removed.

Q: Which of the following is not a restriction for a table to be a relation?

Correct answer: The columns must be ordered.Column order is precisely what a relation does not require: attributes are identified by name, so the columns may be written in any sequence without changing the relation. The other three are genuine requirements - single-valued cells, homogeneous columns, and no duplicate rows - and a table that breaks any of them is not a relation.

Q: In a relation, the rows are sometimes called "records."

Correct answer: TrueThe vocabularies correspond directly: relation, tuple and attribute in the formal relational terminology are table, record and field in the older file-processing one. The terms are used interchangeably in practice, and being fluent in both matters because textbooks and product documentation mix them freely.

Q: If attribute A determines both attributes B and C, then it is also true that:

Correct answer: A → B.If A determines the pair (B, C), then it determines each of them separately: given a value of A, the value of B is fixed and so is the value of C. This is the decomposition rule of Armstrong’s axioms. The converse does not hold, so nothing follows in the reverse direction, and the other three options all reverse the arrow.

Q: A key is a group of one or more attributes that uniquely identifies a row.

Correct answer: TrueThis is the definition of a key. It may consist of a single attribute or of several, in which case it is a composite key, and it must be minimal, so that dropping any attribute from it would destroy uniqueness. A relation may have several such candidate keys, one of which is chosen as the primary key.

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.

81.

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

82.

A relation has cells that hold multi-value entries.

A.True
B.False

Answer: B

Correct answer: False

One of the defining conditions of a relation is that each cell contains a single value. A cell holding several values - a list of phone numbers, say - means the table is not in first normal form and is not a relation at all. The remedy is to move the repeating values into a separate relation.

Discuss in Forum

83.

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

84.

Relations are categorized into normal forms according to the referential integrity constraints that they have.

A.True
B.False

Answer: B

Correct answer: False

Normal forms are defined by the functional and multivalued dependencies a relation permits, not by referential integrity constraints. Referential integrity is a constraint between relations, requiring foreign key values to exist in the referenced relation, and it is entirely independent of how far a relation has been normalised.

Discuss in Forum

85.

Keys made up of two or more attributes are called composite keys.

A.True
B.False

Answer: A

Correct answer: True

A composite key is simply a key made up of more than one attribute, used where no single attribute is unique on its own - a line item identified by order number together with line number, for instance. It is still a key in every respect and must still be minimal, so that no constituent attribute could be removed.

Discuss in Forum

86.

Which of the following is not a restriction for a table to be a relation?

A.The cells of the table must contain a single value.
B.All of the entries in any column must be of the same kind.
C.The columns must be ordered.
D.No two rows in a table may be identical.

Answer: C

Correct answer: The columns must be ordered.

Column order is precisely what a relation does not require: attributes are identified by name, so the columns may be written in any sequence without changing the relation. The other three are genuine requirements - single-valued cells, homogeneous columns, and no duplicate rows - and a table that breaks any of them is not a relation.

Discuss in Forum

87.

In a relation, the rows are sometimes called "records."

A.True
B.False

Answer: A

Correct answer: True

The vocabularies correspond directly: relation, tuple and attribute in the formal relational terminology are table, record and field in the older file-processing one. The terms are used interchangeably in practice, and being fluent in both matters because textbooks and product documentation mix them freely.

Discuss in Forum

88.

If attribute A determines both attributes B and C, then it is also true that:

A.A → B.
B.B → A.
C.C → A.
D.(B,C) → A.

Answer: A

Correct answer: A → B.

If A determines the pair (B, C), then it determines each of them separately: given a value of A, the value of B is fixed and so is the value of C. This is the decomposition rule of Armstrong’s axioms. The converse does not hold, so nothing follows in the reverse direction, and the other three options all reverse the arrow.

Discuss in Forum

89.

A key is a group of one or more attributes that uniquely identifies a row.

A.True
B.False

Answer: A

Correct answer: True

This is the definition of a key. It may consist of a single attribute or of several, in which case it is a composite key, and it must be minimal, so that dropping any attribute from it would destroy uniqueness. A relation may have several such candidate keys, one of which is chosen as the primary key.

Discuss in Forum

90.

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

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