Data Models into Database Designs Questions and Answers

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.

Answer: A

Correct answer: True

A candidate key is any column or set of columns that could serve as the primary key, and once one has been chosen the remainder are the alternate keys. The terms are used interchangeably in this material, and the practical point is that each alternate key should be given a unique constraint so the DBMS enforces its uniqueness too.

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.

Answer: B

Correct answer: False

That describes cascading deletions. Cascading updates propagate a change in the parent’s primary key to the foreign key values referring to it. The two are separate options and are often set differently - cascading updates being harmless with a stable key, cascading deletions being a decision about whether children should survive their parent.

Answer: A

Correct answer: True

A primary key identifies the row, so it must be present in every row and none of its columns may be null. The DBMS enforces this automatically once a primary key is declared, and the rule is entity integrity - the counterpart of referential integrity, which governs foreign keys.

Answer: A

Correct answer: True

Short so that indexes and foreign keys stay compact, numeric so that comparison is fast and the value is compact, and seldom changing so that references to it do not have to be updated. A surrogate key has all three by construction, which is the argument for using one rather than a natural key.

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.

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.

Answer: B

Correct answer: False

There are four sets of minimum cardinalities, since each of the two sides is either optional or mandatory. Six is the number of referential integrity actions to be considered - insert, update and delete on each side - which is a different question and the source of the confusion.

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.