Database Management System Questions and Answers

Answer: A

They are examples of RDBMS.

Oracle Database, MySQL and Microsoft Access are relational database management systems: they store data in tables of rows and columns, link tables through keys, and are queried with SQL.

They are not operating systems, which manage the computer's hardware (Windows, Linux), nor utility software such as antivirus or disk tools. 'Application software' is too broad; the specific class they belong to is RDBMS.

Answer: A

Correct answer: Serializable schedule.

A precedence, or serialization, graph has a node per transaction and an edge for each conflicting pair. If the graph has no cycle the schedule is serializable; a cycle means it is not. Deadlock is detected with a different graph, the wait-for graph.

Answer: B

Correct answer: 3NF

This is the transitive dependency that third normal form forbids: a non-key attribute determining another non-key attribute. Second normal form removes only partial dependencies on part of a composite key, so the relation can satisfy 2NF and still fail here.

Answer: D

Correct answer: All of the above.

Selection can be pushed through any of the three set operations, since deciding whether a tuple satisfies a condition does not depend on which relation it came from:

\[ \sigma_\theta(R \cup S) = \sigma_\theta(R) \cup \sigma_\theta(S) \]

and the same holds for intersection and difference. Doing the selection first is what makes such transformations worth applying.

Answer: C

Correct answer: No partial FDs exist.

Second normal form requires that every non-key attribute depend on the whole of the primary key, so a dependency on only part of a composite key - a partial functional dependency - is what 2NF eliminates. Transitive dependencies are left to 3NF.

Answer: C

Correct answer: DDL

DROP removes a table, view or index - a change to the structure of the database - so it belongs to the Data Definition Language, alongside CREATE and ALTER.

Answer: C

Correct answer: idempotent

Recovery may be interrupted and restarted, so an undo or redo may be applied more than once to the same record. The operations are therefore written to be idempotent: applying them twice leaves the same result as applying them once.

Answer: C

Correct answer: foreign key

A foreign key is a column whose values must appear as a primary key in another table, and that requirement is what represents the relationship between the two. A primary key identifies rows within one table only.

Answer: C

Correct answer: Entity instance

A particular set of attribute values describes one particular thing - one entity instance, or occurrence. The entity set is the collection of all such instances of the same type.

Answer: B

Correct answer: Order by

ORDER BY sorts the result, taking ASC or DESC and one or more columns. GROUP BY collects rows into groups and HAVING filters those groups; neither of them sorts.