Database Management System Questions and Answers

Answer: D

Correct answer: two-phase locking protocol

Cascading rollback happens when one transaction reads data written by another that later aborts. Strict two-phase locking prevents it by holding exclusive locks until commit, and validation-based protocols prevent it by writing only at commit. Plain two-phase locking releases locks as soon as its shrinking phase begins, so uncommitted data can be read and cascading rollback becomes possible.

Answer: D

Correct answer: deadlock detection

A wait-for graph has an edge from each waiting transaction to the one holding the lock it wants; a cycle in that graph means a deadlock, which is then broken by aborting a transaction. Prevention schemes avoid deadlock in advance and need no such graph.

Answer: D

Correct answer: all of the above

ALTER TABLE covers every change to a table's definition: adding a column, dropping one, and changing a column's type, default or constraints.

Answer: D

Correct answer: Logical, physical and view

The ANSI/SPARC three-schema architecture has an internal or physical schema, a conceptual or logical schema, and external or view schemas - one per user group. Separating them is what makes data independence possible.

Answer: B

Correct answer: Multi-valued dependency

If one key has two independent one-to-many relationships in the same table, every combination of the two sets of values must be stored, and the two sets are unrelated to each other. That is a multi-valued dependency, and removing it is what fourth normal form is for.

Answer: D

Correct answer: Primary key

A table may have several candidate keys and several unique constraints, but exactly one of them is designated the primary key. The others are then alternate keys.

Answer: A

Correct answer: BCNF

Every relation can be decomposed into 3NF while keeping all its functional dependencies, but a decomposition into BCNF may not be able to preserve them all. That is the one guarantee BCNF gives up in exchange for removing every remaining redundancy.

Answer: B

Correct answer: Direct

With direct, or hashed, organisation a record's position is computed from its key, so an insertion or deletion touches only that position. A sequential file must be rewritten to keep its order, and an index-sequential file must maintain its index as well.

Answer: C

Correct answer: Relational algebra

Relational algebra is the basic set of operations for manipulating relations - selection, projection, union, difference, product and join. Relational calculus describes results without operations, and SQL is a language built on top of the algebra.

Answer: A

Correct answer: All of the above

All three are genuine advantages. A view can omit columns a user should not see, present computed columns that exist nowhere in the base tables, and stand in for a complicated query so that users need write only a simple one against it.