The Relational Model and Normalization Questions and Answers

Answer: A

Correct answer: True

Attributes are identified by name, so writing the columns in a different order produces the same relation. The same is true of rows, which form a set and so have no inherent order either. Both facts follow from the relation being defined by its content rather than by any arrangement of it.

Answer: A

Correct answer: True

A functional dependency relates attributes within a relation: given a value of the determinant, the value of the dependent attribute is fixed. It is not a relationship between tables - that is what a foreign key expresses - nor between rows. Functional dependencies are the language in which every normal form is defined.

Answer: A

Correct answer: True

First normal form forbids repeating groups and multi-valued entries, requiring each cell to hold a single indivisible value. A column storing a comma-separated list of phone numbers violates it.

Answer: A

Correct answer: True

This is the definition of a key. It may consist of a single attribute or of several, in which case it is a composite key, and it must be minimal, so that dropping any attribute from it would destroy uniqueness. A relation may have several such candidate keys, one of which is chosen as the primary key.

Answer: A

Correct answer: True

A composite key is simply a key made up of more than one attribute, used where no single attribute is unique on its own - a line item identified by order number together with line number, for instance. It is still a key in every respect and must still be minimal, so that no constituent attribute could be removed.

Answer: A

Correct answer: True

In R → S, R is the determinant and S the dependent attribute: R is what fixes the value of S. Every key is a determinant, since identifying a row fixes all its attributes, but the converse fails - and a determinant that is not a candidate key is precisely the violation Boyce-Codd Normal Form forbids.

Answer: B

Correct answer: False

Normal forms are defined by the functional and multivalued dependencies a relation permits, not by referential integrity constraints. Referential integrity is a constraint between relations, requiring foreign key values to exist in the referenced relation, and it is entirely independent of how far a relation has been normalised.

Answer: B

Correct answer: False

Boyce-Codd Normal Form requires that every determinant be a candidate key, and says nothing about whether that key is composite. A single-attribute key is perfectly acceptable. The condition exists because a determinant that is not a candidate key allows the same fact to be stored in many rows, which is the source of update anomalies.

Answer: B

Correct answer: False

A functional dependency is a constraint, not an equation: R → S asserts that each value of R is associated with exactly one value of S, with no arithmetic implied. The values may be names, dates or codes with no numerical relationship at all. The arrow is a statement about determination, not about calculation.

Answer: B

Correct answer: False

One of the defining conditions of a relation is that each cell contains a single value. A cell holding several values - a list of phone numbers, say - means the table is not in first normal form and is not a relation at all. The remedy is to move the repeating values into a separate relation.