The Relational Model and Normalization Questions and Answers

Answer: D

Correct answer: attributes.

A functional dependency is a statement about attributes within a relation: given a value of the determining attribute, the value of the dependent one is fixed. It is a property of the meaning of the data rather than of the rows that happen to be stored, so it cannot be established by inspecting a sample - only refuted by one.

Answer: A

Correct answer: True

Splitting data across more, narrower relations removes duplication and the update anomalies that come with it, but reassembling the information then requires joins. This trade-off is why analytical systems often denormalise deliberately.

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: A

Correct answer: True

A relation exists to record which values go with which, and every such association is a functional dependency - the key determines the non-key attributes. Seen that way, storing instances of functional dependencies is what a relation does, and a relation that stores dependencies belonging to more than one theme is exactly the one that suffers modification anomalies.

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: False

A relation may have several candidate keys, but exactly one of them is designated the primary key and the rest become alternate keys. What can involve several columns is a composite primary key, which is still a single key.

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: C

Correct answer: referential integrity constraint.

A referential integrity constraint requires that every value appearing in a foreign key already exist as a key value in the referenced relation. It is what prevents an order from referring to a customer who does not exist, and it is enforced by the database rather than by the application. Normal forms and anomalies concern the structure of a single relation.

Answer: C

Correct answer: candidate keys.

A candidate key is any minimal set of attributes that uniquely identifies a row, and a relation may have several. The designer selects one of them as the primary key; the rest remain candidate keys and are usually given unique constraints. Foreign keys reference a key in another relation, and determinants need not be unique at all.

Answer: A

Correct answer: column of a table.

An attribute is a column, corresponding to a field in file-processing terms, and it draws its values from a single domain. A row is a tuple, and the whole two-dimensional structure is the relation. A key is a role that one or more attributes play rather than a structural element in its own right.