A relation can have more than one primary key.
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.
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Given the functional dependency R → S , R is called the determinant.
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.
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When the values in one or more attributes being used as a foreign key must exist in another set of one or more attributes in another table, we have created a(n):
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.
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The primary key is selected from the:
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.
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An attribute is a(n):
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.
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Table is synonymous with the term:
Answer: B
Correct answer: relation.
Table, relation and file name the same structure in three vocabularies, just as row, tuple and record do, and column, attribute and field. The relational terms are the formal ones and the ones in which the normal forms are defined, which is why they are worth using precisely even when a product’s documentation does not.
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The different classes of relations created by the technique for preventing modification anomalies are called:
Answer: A
Correct answer: normal forms.
The normal forms are the successive classes of relation defined by which dependencies they still permit, each one eliminating a further source of insertion, deletion and update anomaly. Functional dependencies are what the definitions are stated in terms of, and referential integrity is a separate constraint between relations rather than a class of relation.
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A tuple is a(n):
Answer: C
Correct answer: row of a table.
A tuple is a row, the record of the older vocabulary. Since no two rows in a relation may be identical and the order of rows carries no meaning, a relation is formally a set of tuples - which is why a query result has no inherent ordering unless one is requested explicitly.
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A column that forms part of a foreign key can never contain a NULL value.
Answer: B
Correct answer: False
Referential integrity requires only that a non-null foreign key match an existing primary key value. A NULL is permitted and simply means the relationship is unknown or does not apply, unless the column is separately declared NOT NULL.
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A candidate key is a determinant that determines all the other columns is a relation.
Answer: A
Correct answer: True
A candidate key is a minimal set of attributes that uniquely identifies a row, and identifying the row fixes the value of every attribute in it - so the key functionally determines every other column. This is why candidate keys are determinants; the point of Boyce-Codd Normal Form is to insist that every determinant be one of them.
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