Logical Database Design Questions and Answers

Q: When converting an E-R diagram to a relational schema, how is a multivalued attribute typically represented in the relational model ?

A multivalued attribute becomes a separate relation with a foreign key.A relation in first normal form cannot store several values in one column. So a multivalued attribute, such as an employee's several phone numbers, is moved to a new relation holding the owning entity's key (as a foreign key) and the attribute value, for example EMP_PHONE(emp_id, phone), with the two columns together as its primary key. Each value becomes its own row.A composite attribute is a different idea (one value with parts, like an address) and is flattened into several columns. A nullable column in the same table can hold only one value. CHECK constraints validate values and do nothing to store several of them.

Q: What is a surrogate key in database design ?

A surrogate key is a system-generated unique identifier.A surrogate key, such as an auto-increment integer or a UUID, is created by the database purely to identify rows and carries no business meaning. It stays stable even if real-world values such as names or e-mail addresses change, which makes it a convenient primary key.A natural key comes from the data itself, such as an Aadhaar or ISBN number, which is the opposite of a surrogate. A composite key combines several columns. A foreign key refers to the key of another table.

Q: When mapping a many-to-many unary relationship into a relation which of the following is true?

Correct answer: Two relations are created.A unary many-to-many relationship - a part composed of other parts, an employee supervising employees - needs the entity’s own relation plus an associative relation holding pairs of its key. The associative relation’s key is the two roles taken together, each a foreign key to the same relation.

Q: The primary key in a relation does not need to be underlined.

Correct answer: FalseUnderlining the primary key is the standard convention for writing a relation, and it is how a reader tells the key from the other attributes. Foreign keys are conventionally marked too, usually by a dashed underline or an italic. The notation carries information rather than decorating it.

Q: A foreign key may be null and still adhere to the referential integrity constraint.

Correct answer: TrueA null foreign key means the row participates in no relationship, which is exactly how optional participation is expressed. Referential integrity requires only that a foreign key which does hold a value must match an existing primary key - it does not require a value to be present.

Q: If no multivalued attributes exist and no partial dependencies exist in a relation, then the relation is in what normal form?

Correct answer: Second normal formSecond normal form requires first normal form, which is what the absence of multivalued attributes gives, plus the absence of partial dependencies on part of a composite key. Third normal form would need transitive dependencies removed as well, and nothing here says they have been.

Q: The primary key of the new relation in a many-to-many relationship is a composite key comprised of the primary keys of each of the binary entities.

Correct answer: TrueThe associative relation’s primary key is the two foreign keys taken together, since a pairing is identified by which two rows it joins. Where the same pair may recur - the same student enrolling on the same course twice - a further attribute such as a date must be added to keep the key unique.

Q: Weak entities do not get mapped into a relation.

Correct answer: FalseA weak entity does become a relation. What distinguishes it is the primary key: the partial identifier of the weak entity combined with the primary key of the owner, which is also a foreign key. That composite key is what expresses the existence dependence in the relational model.

When converting an E-R diagram to a relational schema, how is a multivalued attribute typically represented in the relational model ?

A.As a composite attribute
B.As a nullable column in the same table
C.As an attribute with CHECK constraints
D.As a separate relation with a foreign key

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: D

A multivalued attribute becomes a separate relation with a foreign key.

A relation in first normal form cannot store several values in one column. So a multivalued attribute, such as an employee's several phone numbers, is moved to a new relation holding the owning entity's key (as a foreign key) and the attribute value, for example EMP_PHONE(emp_id, phone), with the two columns together as its primary key. Each value becomes its own row.

A composite attribute is a different idea (one value with parts, like an address) and is flattened into several columns. A nullable column in the same table can hold only one value. CHECK constraints validate values and do nothing to store several of them.

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What is a surrogate key in database design ?

A.A natural key from the data
B.A system-generated unique identifier
C.A composite key
D.A foreign key reference

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: B

A surrogate key is a system-generated unique identifier.

A surrogate key, such as an auto-increment integer or a UUID, is created by the database purely to identify rows and carries no business meaning. It stays stable even if real-world values such as names or e-mail addresses change, which makes it a convenient primary key.

A natural key comes from the data itself, such as an Aadhaar or ISBN number, which is the opposite of a surrogate. A composite key combines several columns. A foreign key refers to the key of another table.

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Based on the cardinality ratio and participation ________ associated with a relationship type, choose either the Foreign Key Design, the Cross Referencing Design or Mutual Referencing Design.

A.Entity
B.Constraints
C.Rules
D.Keys

Exam Year(s)

UGC NET - 2013,

Answer: B

The word needed is 'Constraints'. The choice between the foreign key design, the cross-referencing design and the mutual referencing design when mapping an ER relationship to tables depends on the cardinality ratio and the participation constraints (total or partial) of the relationship type.

'Entity', 'Rules' and 'Keys' do not form a standard phrase here. The text 'participation constraints' is the term used in ER-to-relational mapping, and keys are what the designs then use, not what the choice is based on.

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When mapping a many-to-many unary relationship into a relation which of the following is true?

A.One relation is created.
B.Two relations are created.
C.Three relations are created.
D.Four relations are created.

Answer: B

Correct answer: Two relations are created.

A unary many-to-many relationship - a part composed of other parts, an employee supervising employees - needs the entity’s own relation plus an associative relation holding pairs of its key. The associative relation’s key is the two roles taken together, each a foreign key to the same relation.

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The primary key in a relation does not need to be underlined.

A.True
B.False

Answer: B

Correct answer: False

Underlining the primary key is the standard convention for writing a relation, and it is how a reader tells the key from the other attributes. Foreign keys are conventionally marked too, usually by a dashed underline or an italic. The notation carries information rather than decorating it.

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A foreign key may be null and still adhere to the referential integrity constraint.

A.True
B.False

Answer: A

Correct answer: True

A null foreign key means the row participates in no relationship, which is exactly how optional participation is expressed. Referential integrity requires only that a foreign key which does hold a value must match an existing primary key - it does not require a value to be present.

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If no multivalued attributes exist and no partial dependencies exist in a relation, then the relation is in what normal form?

A.First normal form
B.Second normal form
C.Third normal form
D.Fourth normal form

Answer: B

Correct answer: Second normal form

Second normal form requires first normal form, which is what the absence of multivalued attributes gives, plus the absence of partial dependencies on part of a composite key. Third normal form would need transitive dependencies removed as well, and nothing here says they have been.

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When mapping a supertype/subtype relationship which of the following is true?

A.The supertype primary key is assigned to each subtype.
B.The subtype primary key is assigned to each supertype.
C.There is no link between the supertype/subtype entities.
D.There is no primary key/foreign key relationship between a supertype/subtype.

Answer: A

Correct answer: The supertype primary key is assigned to each subtype.

Each subtype becomes a relation whose primary key is the supertype’s primary key, which is also a foreign key referring back to it. This is what makes the subtype row and the supertype row the same entity seen twice, and it is why a subtype instance cannot exist without its supertype instance.

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The primary key of the new relation in a many-to-many relationship is a composite key comprised of the primary keys of each of the binary entities.

A.True
B.False

Answer: A

Correct answer: True

The associative relation’s primary key is the two foreign keys taken together, since a pairing is identified by which two rows it joins. Where the same pair may recur - the same student enrolling on the same course twice - a further attribute such as a date must be added to keep the key unique.

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10.

Weak entities do not get mapped into a relation.

A.True
B.False

Answer: B

Correct answer: False

A weak entity does become a relation. What distinguishes it is the primary key: the partial identifier of the weak entity combined with the primary key of the owner, which is also a foreign key. That composite key is what expresses the existence dependence in the relational model.

Discuss in Forum

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