Data Models into Database Designs Questions and Answers

Answer: A

Correct answer: True

An intersection table exists only to record that a particular parent on one side is associated with a particular parent on the other, so it cannot exist independently of either. Its primary key is the combination of the two foreign keys, which is exactly what makes it ID-dependent on both.

Answer: C

Correct answer: primary key

The transformation is direct: each entity becomes a table, each attribute becomes a column, and the entity’s identifier becomes the table’s primary key. That correspondence is what makes the relational design follow mechanically from a well-made data model, with the relationships then represented by foreign keys.

Answer: D

Correct answer: Six

Enforcing a minimum cardinality means constraining what may be done, and there are three actions on each side of the relationship - insert, update and delete on the parent, and the same three on the child - giving six in all. Each must be considered separately when the design is worked out, since a rule that protects one direction may say nothing about the other.

Answer: A

Correct answer: True

This is the first rule of the transformation: one table per entity, one column per attribute, the identifier becoming the primary key. Relationships are then added as foreign keys, and many-to-many relationships require an intersection table of their own, which is the one place where a table appears without a corresponding entity.

Answer: C

Correct answer: An intrarelation constraint

Intra means within: the constraint compares two columns of the same row in the same table, as in requiring a discounted price to be less than the list price. An interrelation constraint compares values across tables, a domain constraint enumerates permitted values, and a range constraint bounds one column between limits.

Answer: D

Correct answer: Data constraints

Comparing one column against another in the same row is beyond what a type or a default can express, so it is a data constraint - specifically an intrarelation constraint, since both columns lie in the same table. The data type would establish only that both are monetary values.

Answer: B

Correct answer: False

A surrogate key is assigned by the DBMS and is not made available for alteration. That immutability is the whole point: because the key never changes, no cascading update is ever needed and no reference to it can become stale. A key the application could change would forfeit that advantage.

Answer: A

Correct answer: the primary key

Cascading updates propagate a change in the parent’s primary key to every foreign key value referring to it, so that the references stay valid. The provision is only needed where the primary key can change; a surrogate key never does, which is exactly why using one makes cascading updates unnecessary.

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.

Answer: A

Correct answer: True

A parent needs no child in order to exist, whatever the child’s minimum cardinality demands of the parent, so a new parent row may always be inserted. It is the child that cannot be inserted freely when the parent is required, since it must have a parent to refer to.