Database Design Using Normalization Questions and Answers

Q: When building a database from an existing set of tables, we may safely assume that referential integrity constraints have been enforced on the data we are given.

Correct answer: FalseData arriving from an existing system may have been maintained by applications that never enforced the constraints, or by none at all, so orphaned foreign key values are common. This is exactly why assessing the validity of the assumed referential integrity constraints is a separate step in examining acquired tables rather than something to be taken on trust.

Q: One common design problem when designing a database from existing data is the presence of inconsistent values in the received data.

Correct answer: TrueInconsistent values - the same thing recorded in different ways, with variant spellings, word orders or punctuation - are among the commonest problems in received data. They break grouping, counting and joining, and the standard way of exposing them is a GROUP BY on the column, which puts each variant in its own group.

Q: A relation is a two-dimensional table.

Correct answer: TrueA relation is a two-dimensional table with the further restrictions that each cell holds a single value, all entries in a column are of one kind, no two rows are identical, and neither row nor column order carries meaning. A table meeting all of them is a relation; one that does not is merely a table.

Q: Multivalued dependencies should ________ be eliminated.

Correct answer: alwaysA multivalued dependency means one relation is carrying two independent multivalued facts about the same key, which forces every combination of the two to be stored and produces genuine anomalies. Splitting the relation so that each holds a single theme removes them entirely, at no cost in information, so there is no reason to tolerate one.

51.

When building a database from an existing set of tables, we may safely assume that referential integrity constraints have been enforced on the data we are given.

A.True
B.False

Answer: B

Correct answer: False

Data arriving from an existing system may have been maintained by applications that never enforced the constraints, or by none at all, so orphaned foreign key values are common. This is exactly why assessing the validity of the assumed referential integrity constraints is a separate step in examining acquired tables rather than something to be taken on trust.

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52.

One common design problem when designing a database from existing data is the presence of inconsistent values in the received data.

A.True
B.False

Answer: A

Correct answer: True

Inconsistent values - the same thing recorded in different ways, with variant spellings, word orders or punctuation - are among the commonest problems in received data. They break grouping, counting and joining, and the standard way of exposing them is a GROUP BY on the column, which puts each variant in its own group.

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53.

A relation is a two-dimensional table.

A.True
B.False

Answer: A

Correct answer: True

A relation is a two-dimensional table with the further restrictions that each cell holds a single value, all entries in a column are of one kind, no two rows are identical, and neither row nor column order carries meaning. A table meeting all of them is a relation; one that does not is merely a table.

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54.

Each answer below shows example data from a table. Which answer is an example of the multivalue, multicolumn problem?

A.Three columns have the values 534-2435, 534-7867, and 546-2356 in the same row.
B.Three rows have the values Brown Small Chair, Small Chair Brown, and Small Brown Chair in the same column.
C.Three rows have the values Brown, NULL, and Blue in the same column.
D.One row has the value "He is interested in a Silver Porsche from the years 1978-1988" in a column.

Answer: A

Correct answer: Three columns have the values 534-2435, 534-7867, and 546-2356 in the same row.

This is the multivalue, multicolumn problem: several values of the same attribute - here telephone numbers - held in a row of separate columns. It fails because the number of columns is fixed while the number of values is not, and because querying across them requires the same condition to be repeated for each. The values belong in a separate table, one row each.

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55.

Multivalued dependencies should ________ be eliminated.

A.always
B.commonly
C.seldom
D.never

Answer: A

Correct answer: always

A multivalued dependency means one relation is carrying two independent multivalued facts about the same key, which forces every combination of the two to be stored and produces genuine anomalies. Splitting the relation so that each holds a single theme removes them entirely, at no cost in information, so there is no reason to tolerate one.

Discuss in Forum

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Database Design Using Normalization Questions and Answers

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