Database Design Using Normalization Questions and Answers

Q: One common design problem when designing a database from existing data is the use of a general-purpose remarks column in the received data.

Correct answer: TrueA general-purpose remarks column collects whatever users think worth noting, so it holds different kinds of fact in different rows, in free text that cannot be validated or queried. It is one of the standard problems in received data, and the remedy is to identify what is actually being recorded there and give each item a column of its own.

Q: We use the SQL construct COLUMNS(*) to determine the number and type of columns in a table.

Correct answer: FalseThere is no such SQL construct. The number and type of columns in a table are found by querying the system catalog or the information schema, or by using a product-specific command such as DESCRIBE or sp_columns. COUNT(*) does exist and counts rows, which is probably what the invented name is meant to echo.

Q: When building a database from an existing set of tables, we may safely assume that there are no multivalued dependencies in the data we are given.

Correct answer: FalseNothing about received data guarantees the absence of multivalued dependencies; the tables were designed by someone else, possibly with no normalization at all. Their presence must be established by examining the data and understanding what it means, and where one is found the relation should be split so that each holds a single theme.

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

Correct answer: FalseThe statement is right about the problem and wrong about its name. Missing values are called null values, not blank values, and the distinction matters because a null is not an empty string - it is the absence of a value, and it may mean unknown, not applicable, or simply not yet entered.

Q: When assessing the table structure of an acquired set of tables with data, determining functional dependencies is (part of) the:

Correct answer: second step.The second step is where the structure is inferred: the functional dependencies among the columns, and from them the primary keys, and then the foreign keys that link the tables. The first step is only a survey of what has arrived, and the third checks whether the implied referential integrity constraints are actually satisfied.

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.

41.

One common design problem when designing a database from existing data is the use of a general-purpose remarks column in the received data.

A.True
B.False

Answer: A

Correct answer: True

A general-purpose remarks column collects whatever users think worth noting, so it holds different kinds of fact in different rows, in free text that cannot be validated or queried. It is one of the standard problems in received data, and the remedy is to identify what is actually being recorded there and give each item a column of its own.

Discuss in Forum

42.

We use the SQL construct COLUMNS(*) to determine the number and type of columns in a table.

A.True
B.False

Answer: B

Correct answer: False

There is no such SQL construct. The number and type of columns in a table are found by querying the system catalog or the information schema, or by using a product-specific command such as DESCRIBE or sp_columns. COUNT(*) does exist and counts rows, which is probably what the invented name is meant to echo.

Discuss in Forum

43.

When building a database from an existing set of tables, we may safely assume that there are no multivalued dependencies in the data we are given.

A.True
B.False

Answer: B

Correct answer: False

Nothing about received data guarantees the absence of multivalued dependencies; the tables were designed by someone else, possibly with no normalization at all. Their presence must be established by examining the data and understanding what it means, and where one is found the relation should be split so that each holds a single theme.

Discuss in Forum

44.

One common design problem when designing a database from existing data is the presence of missing values, called blank values, in received data.

A.True
B.False

Answer: B

Correct answer: False

The statement is right about the problem and wrong about its name. Missing values are called null values, not blank values, and the distinction matters because a null is not an empty string - it is the absence of a value, and it may mean unknown, not applicable, or simply not yet entered.

Discuss in Forum

45.

When assessing the table structure of an acquired set of tables with data, determining functional dependencies is (part of) the:

A.first step.
B.second step.
C.third step.
D.fourth step

Answer: B

Correct answer: second step.

The second step is where the structure is inferred: the functional dependencies among the columns, and from them the primary keys, and then the foreign keys that link the tables. The first step is only a survey of what has arrived, and the third checks whether the implied referential integrity constraints are actually satisfied.

Discuss in Forum

46.

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.

Discuss in Forum

47.

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.

Discuss in Forum

48.

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.

Discuss in Forum

49.

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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50.

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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