Data Models into Database Designs Questions and Answers

Q: Which of the following data constraints would be used to specify that the value of cells in a column must be one of a specific set of possible values?

Correct answer: A domain constraintA domain constraint restricts a column to a specified set of permitted values, so that only those values may be stored. A range constraint bounds the value between limits rather than enumerating it, an intrarelation constraint compares columns within one table, and an interrelation constraint compares across tables.

Q: In a 1:N relationship, the foreign key is placed in:

Correct answer: the child table.The foreign key always goes on the many side. Each child row points to one parent, so a single foreign key column suffices; putting it in the parent would require room for an unknown number of child references in one row, which a relation cannot provide. That asymmetry is what makes parent and child meaningful in a 1:N relationship.

Q: Which of the following column properties specifies whether or not cells in a column must contain a data value?

Correct answer: Null statusNull status states whether a column may be left empty. It is one of the four column properties, alongside the data type, which says what kind of value may be stored; the default value, which says what to store if none is supplied; and the data constraints, which limit which values are acceptable.

Q: A primary key should be defined as:

Correct answer: NOT NULL.A primary key identifies a row, and a null cannot identify anything, so every part of a primary key must be present in every row. The DBMS enforces this automatically when a primary key is declared, and entity integrity is the name given to the rule.

Q: Which of the following column properties would be used to specify that cells in a column must contain a monetary value?

Correct answer: Data typeRequiring a monetary value is a matter of the data type - a numeric type with a suitable precision and scale, chosen so that money is stored exactly rather than in binary floating point. Requiring a particular value would be a default, and requiring it to satisfy a condition would be a constraint.

Q: Which of the following situation requires the use of ID-dependent entities?

Correct answer: All of the above use ID dependent entitiesAn ID-dependent entity cannot exist without its parent and takes the parent’s identifier as part of its own. All three cases have that character: an association relationship carries data of its own on an intersection between two parents, a multivalued attribute becomes a table dependent on the entity it describes, and an archetype and its instances stand in the same relation.

Q: Which of the following columns is(are) are required in a table?

Correct answer: A primary keyEvery table must have a primary key, since without one its rows cannot be identified and duplicates cannot be prevented. Foreign keys appear only where the table participates as a child in a relationship, alternate keys only where more than one candidate exists, and a surrogate key only where one has been introduced deliberately.

Q: Which of the following column properties would be used to specify that cells in a column must be immediately filled with a monetary value of $10,000?

Correct answer: Default valueA default value is what the DBMS supplies when the application provides none, so specifying that the cell must be filled immediately with a particular amount is a default. The data type would settle that it is money, and a constraint would limit which amounts are acceptable, but neither puts a value there.

Which of the following data constraints would be used to specify that the value of cells in a column must be one of a specific set of possible values?

A.A domain constraint
B.A range constraint
C.An intrarelation constraint
D.An interrelation constraint

Answer: A

Correct answer: A domain constraint

A domain constraint restricts a column to a specified set of permitted values, so that only those values may be stored. A range constraint bounds the value between limits rather than enumerating it, an intrarelation constraint compares columns within one table, and an interrelation constraint compares across tables.

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In a 1:N relationship, the foreign key is placed in:

A.either table without specifying parent and child tables.
B.the parent table.
C.the child table.
D.either the parent table or the child table.

Answer: C

Correct answer: the child table.

The foreign key always goes on the many side. Each child row points to one parent, so a single foreign key column suffices; putting it in the parent would require room for an unknown number of child references in one row, which a relation cannot provide. That asymmetry is what makes parent and child meaningful in a 1:N relationship.

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Which of the following column properties specifies whether or not cells in a column must contain a data value?

A.Null status
B.Data type
C.Default value
D.Data constraints

Answer: A

Correct answer: Null status

Null status states whether a column may be left empty. It is one of the four column properties, alongside the data type, which says what kind of value may be stored; the default value, which says what to store if none is supplied; and the data constraints, which limit which values are acceptable.

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A primary key should be defined as:

A.NULL.
B.NOT NULL.
C.Either of the above can be used.
D.None of the above are correct.

Answer: B

Correct answer: NOT NULL.

A primary key identifies a row, and a null cannot identify anything, so every part of a primary key must be present in every row. The DBMS enforces this automatically when a primary key is declared, and entity integrity is the name given to the rule.

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Which of the following column properties would be used to specify that cells in a column must contain a monetary value?

A.Null status
B.Data type
C.Default value
D.Data constraints

Answer: B

Correct answer: Data type

Requiring a monetary value is a matter of the data type - a numeric type with a suitable precision and scale, chosen so that money is stored exactly rather than in binary floating point. Requiring a particular value would be a default, and requiring it to satisfy a condition would be a constraint.

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Which of the following situation requires the use of ID-dependent entities?

A.Association relationships only
B.Multivalued attributes only
C.Archetype/instance relationships only
D.All of the above use ID dependent entities

Answer: D

Correct answer: All of the above use ID dependent entities

An ID-dependent entity cannot exist without its parent and takes the parent’s identifier as part of its own. All three cases have that character: an association relationship carries data of its own on an intersection between two parents, a multivalued attribute becomes a table dependent on the entity it describes, and an archetype and its instances stand in the same relation.

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A foreign key is:

A.a column containing the primary key of another table.
B.used to define data types.
C.used to define null status.
D.all of the above are above correct.

Answer: A

Correct answer: a column containing the primary key of another table.

A foreign key is a column, or set of columns, holding values that appear as the primary key of some table - often another, though a recursive relationship makes it the same one. It is the sole mechanism by which relationships are represented, since the relational model has no pointers and every link is expressed by matching values.

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Which of the following columns is(are) are required in a table?

A.A foreign key
B.An alternate key
C.A primary key
D.A surrogate key.

Answer: C

Correct answer: A primary key

Every table must have a primary key, since without one its rows cannot be identified and duplicates cannot be prevented. Foreign keys appear only where the table participates as a child in a relationship, alternate keys only where more than one candidate exists, and a surrogate key only where one has been introduced deliberately.

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In a 1:1 relationship, the foreign key is placed in:

A.either table without specifying parent and child tables.
B.the parent table.
C.the child table.
D.either the parent table or the child table.

Answer: A

Correct answer: either table without specifying parent and child tables.

In a one-to-one relationship each row on either side matches at most one on the other, so a single foreign key column serves whichever table it is placed in. There is no many side to force the choice, and the decision is made on practical grounds - which table is more often queried, or which participation is optional.

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10.

Which of the following column properties would be used to specify that cells in a column must be immediately filled with a monetary value of $10,000?

A.Null status
B.Data type
C.Default value
D.Data constraints

Answer: C

Correct answer: Default value

A default value is what the DBMS supplies when the application provides none, so specifying that the cell must be filled immediately with a particular amount is a default. The data type would settle that it is money, and a constraint would limit which amounts are acceptable, but neither puts a value there.

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