Database Management System Questions and Answers

Answer: C

Correct answer: transaction manager

The transaction manager ensures that every transaction takes the database from one consistent state to another, committing all of its changes or none of them. The buffer and file managers move pages, and the integrity manager checks constraints on individual operations.

Answer: C

Correct answer: Schema

A schema is the description of a relation's structure: its attributes and the domain of each. An instance is the set of tuples present at a given moment, which changes while the schema stays fixed.

Answer: D

Correct answer: 3NF

Third normal form removes both partial and transitive dependencies and can always be reached without losing any functional dependency, which is why it is the normal form ordinarily aimed at. BCNF is stronger but may not be dependency preserving, and 4NF and 5NF address problems that arise less often.

Answer: C

Correct answer: Both of them

Both forms are valid. Naming the columns explicitly is safer, because the statement then does not depend on the order in which the columns were defined; omitting the list requires a value for every column in table order.

Answer: C

Correct answer: Domain

A limit on the values a single attribute may take is a domain constraint - here, that salary must not exceed $10000. A tuple constraint would relate two attributes of the same row, and a schema constraint the structure itself.

Answer: A

Correct answer: Chain

The three logical database structures are hierarchical (tree), network and relational. A chain is a way of linking records physically, not a logical model of the data.

Answer: C

Correct answer: Hierarchical model.

The hierarchical model arranges records in a tree, each child having exactly one parent. The network model uses a graph, which allows several parents, and the relational model uses tables with no structural links at all.

Answer: A

Correct answer: Referential constraint.

A referential integrity constraint requires every value of a foreign key to appear as a key value in the referenced table, so no reference points at a row that does not exist. Integrity constraint is the general category, of which this is one kind.

Answer: D

Correct answer: Select

Union, intersection and Cartesian product are all operations of set theory, applied here to relations. Selection is peculiar to relational algebra: it picks the tuples that satisfy a predicate, which set theory has no notion of.

Answer: C

Correct answer: mn and 0

A join is a subset of the Cartesian product, so at most every pair of rows matches, giving \( m \times n \) tuples; and at fewest no pair matches, giving 0. The extremes are the product and the empty relation.