# MCQ Practice questions in DBMS with answers explained, important questions in database management systems for exams

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__MCQ Quiz Questions and Answers in DBMS__

*1. What property of decompositions is guaranteed by both BCNF and 3NF?*
a) Lossless join
decomposition

b) Lossy join
decomposition

c) Dependency
preserving decomposition

d) All of the above

**View Answer**Answer: (a)
Lossless join decompositionBCNF and 3NF
decompositions can guarantee only the lossless join decomposition.3NF
decompositions alone can be both lossless join and dependency preserving
decomposition. But for BCNF it is lossless join decomposition but not
necessarily (not always) a dependency preserving. |

*2. Which of the following are active database elements?*
a) Functions

b) Constraints

c) Triggers

d) Views

**View Answer**Answer: (b) Constraints
and (c) TriggersConstraints are
considered as active database elements because you cannot violate them at any
point in time. For example, if you have designated an attribute as primary
key in a table, you cannot enter a duplicate value for that attribute ever.Triggers are the
mechanisms to make sure the steps to be taken if an conditions are met in a
table during data manipulation in general. |

*3. Consider a relation R(A, B, C, D, E) with FD set S = {A → BC, CD → E, B → D, E → A}. If R is decomposed into two relations, which of the following is a lossless join decomposition?*
a) (ABC), (CDE)

b) (ABD), (BCE)

c) (ABC), (ADE)

d) None of the
above

**View Answer**Answer: (c) (ABC),
(ADE)A decomposition
of R into R_{1} and R_{2} is a lossless-join decomposition if
any one of the following functional dependency holds: R_{1} ∩ R_{2}
→ R_{1} R_{1} ∩ R_{2}
→ R_{2}Let us check for
these functional dependencies for the answer.(ABC) ∩ (ADE) = AIs it true that A
→ ABC? YES. Using the FD A → BC, this is true.Is it true that A
→ ADE? NO. But to decide the
lossless join decomposition property, only one condition can be true. |

*4. Which of the following views are updatable?*
a) Views created
from single relation

b) Views created
from joining of two tables

c) Views that
included aggregate functions

d) All of the above

**View Answer**Answer: (a) Views
created from single relationViews created
from single relation can be updateable, that too with certain conditions.We can’t update
the other views. |

*5. Assume that we have a relation R(A, B, C, D, E) with a multi-valued dependency A →→ BC (A multi-determines BC). Which of the following statements are correct?*
a) For a given A,
the values of BC and DE are dependent of each other.

b) For a given A,
the values of BC and DE are independent of each other

c) The values of BC
can determine that of DE

d) The values of DE
can determine that of BC

**View Answer**Answer: (b) For a
given A, the values of BC and DE are independent of each other The definition of
multi-valued dependencies:Let R be a
relation schema and let X and Y be subsets of the attributes of R.
Intuitively, the multi-valued dependency X →→ Y is said to
hold over R if in every legal instance r of R, each X value is associated
with a set of Y values and this set is independent of
the values in the other attributes. Example:Let us assume a
relation R(X, Y, Z) with tuples as follows;
In this example X
→→ Y because each X value (x1) is associated
with a set of Y values (y1, y2) and this set is independent of the values of
Z. |

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