Database Management System Questions and Answers

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: Structured query language

SQL stands for Structured Query Language. It is more than a query language, since it also defines and controls data, but the name records its origin.

Answer: A

Correct answer: Constraints

Constraints are declared as part of the table definition, so the DBMS itself enforces them on every operation and no path can bypass them. A trigger can enforce a rule too, but it is code that has to be written correctly and runs after the fact.

Answer: B

Correct answer: a tuple

In relational terminology a row is a tuple, a column is an attribute, and the table as a whole is a relation.

Answer: C

Correct answer: Relations

The relational model stores data in two-dimensional tables called relations, whose rows are tuples and columns attributes. The name comes from the mathematical relation, a set of tuples over given domains.

Answer: C

Correct answer: COUNT

COUNT returns the number of values; SUM adds them. The distinction matters because \( \text{COUNT}(column) \) counts only the non-null values, while \( \text{COUNT}(*) \) counts rows.

Answer: B

Correct answer: Rule

A rule is bound to a column or a user-defined data type and specifies which values are acceptable there. A default supplies a value when none is given, and an index affects only how rows are found.

Answer: C

Correct answer: data is integrated and can be accessed by multiple programs

The point of the database approach is that data is held once, in one place, and shared: many programs read the same integrated store instead of each keeping its own file. Redundancy falls rather than rises, and the data becomes independent of the programs.

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: B

Correct answer: instance of the database

An instance is the data present at a particular moment; the schema is the structure, which stays the same while the instance changes with every insert and delete.