In a relation, the rows are sometimes called "fields."
Answer: B
Correct answer: False
Rows are tuples, or records; it is the columns that are called fields, along with attributes. Getting the correspondence the wrong way round is easy, so it is worth fixing the two triples in mind: relation, table, file for the whole structure; tuple, row, record across; and attribute, column, field down.
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A relation is in Boyce-Codd Normal Form (BCNF) if every determinant is a composite key.
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.
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A relation is in this form if it is in BCNF and has no multivalued dependencies:
Answer: C
Correct answer: fourth normal form.
Fourth normal form adds the elimination of multivalued dependencies to the requirements of Boyce-Codd Normal Form. A multivalued dependency arises when one attribute determines a set of values rather than a single value, and two such independent sets in one relation force every combination to be stored - which is what splitting into separate relations removes.
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In a relation, the order of the rows matters.
Answer: B
Correct answer: False
Row order carries no meaning in a relation: a relation is a set of tuples, and a set has no inherent sequence. A query that needs its output in a particular order must request it explicitly, and any apparent ordering in a result set without such a request is an accident of storage and must not be relied on.
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Given the functional dependency R → (S,T) , then it is also true that R → S.
Answer: A
Correct answer: True
If R determines the pair (S, T), then given a value of R the value of S is fixed - the pair could not be determined otherwise. This is the decomposition rule of Armstrong’s axioms, and it is what allows a dependency on a set of attributes to be broken down into a dependency on each of them separately. The converse does not follow.
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A relation has cells that hold multi-value entries.
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.
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Every relation that is in BCNF is necessarily also in third normal form.
Answer: A
Correct answer: True
The normal forms are nested: BCNF is strictly stronger than 3NF, so satisfying it implies satisfying 3NF. The converse does not hold, since a 3NF relation with overlapping candidate keys can still violate BCNF.
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Relations are categorized into normal forms according to the referential integrity constraints that they have.
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.
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Keys made up of two or more attributes are called composite keys.
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.
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Which of the following is not a restriction for a table to be a relation?
Answer: C
Correct answer: The columns must be ordered.
Column order is precisely what a relation does not require: attributes are identified by name, so the columns may be written in any sequence without changing the relation. The other three are genuine requirements - single-valued cells, homogeneous columns, and no duplicate rows - and a table that breaks any of them is not a relation.
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