The Relational Model and Normalization Questions and Answers

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.

Answer: C

Correct answer: identifies a row.

A key identifies rows, not columns, and it may consist of one attribute or several - a key of two or more is a composite key, but there is no requirement either way. What matters is that the combination be unique across the relation and minimal, so that no attribute could be dropped and uniqueness still hold.

Answer: C

Correct answer: two-dimensional table.

A relation is a two-dimensional structure of rows and columns in which each cell holds a single value, all entries in a column are of one kind, no two rows are identical, and neither the row order nor the column order carries meaning. Those conditions together are what distinguish a relation from a table in the loose sense.