Database short questions part 3 |Gpgc Mardan
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DBMS short questions for interview and exam
41. What is normalization?
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs)
and primary key to achieve the properties.
(1).Minimizing redundancy,
(2). Minimizing insertion, deletion and update anomalies.
42. What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of
R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for
any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X
component of a tuple uniquely determines the value of component Y.
43. What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after
decomposition.
Also read:-
44. What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.
45. What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional
dependency if removal of any attribute A from X means that the dependency does not hold any more.
46. What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully
functionally dependent on primary key.
47. What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
1. X is a Super-key of R.
2. A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
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48. What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X
A, X must be a candidate key.
49. What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one
of following is true.
1.) X is subset or equal to (or) XY = R.
2.) X is a super key.
50. What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one
the following is true.
1.) Ri = R for some i.
2.) The join dependency is implied by the set of FD, over R in which the left side is key of R.
51. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the
constraint can be enforced by simply enforcing the domain constraint and key constraint on
the relation.
52. What are partial, alternate,, artificial, compound and natural key?
1. Partial Key: It is a set of attributes that can uniquely identify weak entities and that
are related to same owner entity. It is sometime called as Discriminator.
2. Alternate Key: All Candidate Keys excluding the Primary Key are known as Alternate Keys.
3. Artificial Key: If no obvious key, either stand alone or compound is available, then the last
resort is to simply create a key, by assigning a unique number to each record or occurrence.
Then this is known as developing an artificial key.
4. Compound Key: If no single data element uniquely identifies occurrences within a construct,
then combining multiple elements to create a unique identifier for the construct is known as
creating a compound key.
5. Natural Key: When one of the data elements stored within a construct is utilized as
the primary key, then it is called the natural key.
53. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
1. Binary search style indexing
2. B-Tree indexing
3. Inverted list indexing
4. Memory resident table
5. Table indexing
54. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about every relation and
index that it contains. This information is stored in a collection of relations maintained by the system
called metadata. It is also called data dictionary.
55. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the least
estimated cost is referred to as query optimization.
56. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects should
persist even if the system crashes before all its changes are reflected on disk. This property is
called durability.
57. What do you mean by atomicity and aggregation?
1. Atomicity: Either all actions are carried out or none are. Users should not have to
worry about the effect of incomplete transactions. DBMS ensures this by undoing the
actions of incomplete transactions.
2. Aggregation: A concept which is used to model a relationship between a collection of entities and
relationships. It is used when we need to express a relationship among relationships.
58. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the
deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called
phantom deadlocks and they lead to unnecessary aborts.
59. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce
the amount of work to be done during restart in the event of subsequent crashes.
60. What are the different phases of transaction?
Different phases are
1.) Analysis phase,
2.) Redo Phase,
3.) Undo phase.