The Relational Model and Normalization Questions and Answers

Answer: A

Correct answer: split the relation into two relations, each with a single theme.

A multivalued dependency problem arises when one relation holds two independent multivalued facts about the same key, forcing every combination of the two to be stored. Separating them into two relations, each carrying a single theme, removes the spurious combinations entirely - and this is exactly what putting the relation into fourth normal form means.

Answer: B

Correct answer: False

Rows are tuples, or records; it is the columns that are called fields, along with attributes. Getting the correspondence the wrong way round is easy, so it is worth fixing the two triples in mind: relation, table, file for the whole structure; tuple, row, record across; and attribute, column, field down.

Answer: B

Correct answer: False

Boyce-Codd Normal Form requires that every determinant be a candidate key, and says nothing about whether that key is composite. A single-attribute key is perfectly acceptable. The condition exists because a determinant that is not a candidate key allows the same fact to be stored in many rows, which is the source of update anomalies.

Answer: C

Correct answer: fourth normal form.

Fourth normal form adds the elimination of multivalued dependencies to the requirements of Boyce-Codd Normal Form. A multivalued dependency arises when one attribute determines a set of values rather than a single value, and two such independent sets in one relation force every combination to be stored - which is what splitting into separate relations removes.

Answer: B

Correct answer: False

Row order carries no meaning in a relation: a relation is a set of tuples, and a set has no inherent sequence. A query that needs its output in a particular order must request it explicitly, and any apparent ordering in a result set without such a request is an accident of storage and must not be relied on.

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.

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.

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.

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.

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.