The Relational Model and Normalization Questions and Answers

Answer: D

Correct answer: Domain/key normal form

Fagin proved that a relation in domain/key normal form has no modification anomalies of any kind, and conversely that any relation free of them is in DK/NF. It is defined by requiring that every constraint on the relation follow from its domain and key definitions alone. The difficulty is that there is no general procedure for putting a relation into it.

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: Key

A key is one or more attributes whose values uniquely identify a row. A determinant is the left-hand side of a functional dependency and need not be unique - every key is a determinant, but not every determinant is a key, and that asymmetry is exactly what Boyce-Codd Normal Form addresses. A tuple is a row and a relation a table.

Answer: B

Correct answer: False

A primary key is chosen from among the candidate keys, and there is no requirement that it be composite - most primary keys are single attributes, and many are deliberately introduced surrogate keys for exactly that reason. A composite key may be selected as the primary key, but that is a possibility rather than part of the definition.

Answer: C

Correct answer: (A,B) is a composite determinant.

When two attributes together determine a third, the pair forms a composite determinant, and the dependency is on the pair as a whole. It does not follow that either attribute determines C on its own - if it did, the other would be redundant and the determinant would not be minimal. Nor does the dependency work in reverse.

Answer: A

Correct answer: record.

The relational model and the older file-processing vocabulary describe the same structures in different words: a relation is a table, a tuple is a row is a record, and an attribute is a column is a field. Knowing the correspondence matters mainly because textbooks and products mix the two vocabularies freely.

Answer: D

Correct answer: foreign keys.

A relationship is represented by placing the key of one relation into another as a foreign key, so a row in the second can be matched to exactly one row in the first. The relational model has no pointers and no explicit links; every relationship is expressed by matching values, which is what allows relations to be joined in any combination.

Answer: A

Correct answer: True

Columns are attributes in the relational vocabulary, fields in the older file-processing one. Each attribute draws its values from a single domain, and attributes are identified by name rather than by position, which is why the order in which the columns are written does not matter.

Answer: A

Correct answer: A → B.

A functional dependency holds when each value of the determinant is always paired with one and the same value of the dependent attribute. Here A always brings the same B, so A determines B; but A appears with different values of C, so A does not determine C, and it cannot determine the pair (B, C) either. The last option reverses the direction, for which the data give no evidence.

Answer: B

Correct answer: False

Isolating multivalued dependencies in their own relations gives fourth normal form, not fifth. Fifth normal form, sometimes called project-join normal form, deals with join dependencies: relations that cannot be reconstructed correctly from any two of their projections but can from three or more.