RDBMS Concepts & Interview Questions by mavvsn reddy

RDBMS
Concepts - Basics & Interview Questions

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A relational database management system (RDBMS)
is a database management system (DBMS) that

utilizes a relational database
model to hold the data used in the application. Short for Relational Database

Management System, RDBMS refers to a
relational database plus supporting software for managing users

and processing SQL queries,
performing backups/restores and associated tasks. RDBMS usually include an

API so that developers can
write programs that use them. Typical RDBMS include Microsoft Access,

Microsoft SQL Server,
Sybase, IBM DB2, Oracle, Ingres, MySQL, Postgresql and many more.

These RDBMS Fundamentals contain the
Basics of RDBMS Concepts to help you prepare for the Interview

of a DBA. Please feel free
to share these RDBMS Interview Questions and Answers with your friends.

RDBMS
Concepts & Interview Questions

1. What is a Database?

A database is a logically coherent collection
of data with some inherent meaning, representing some aspect

of real world and which is
designed, built and populated with data for a specific purpose.

2. What is DBMS?

It is a collection of programs that enables
user to create and maintain a database. In other words it is

general-purpose software that provides
the users with the processes of defining, constructing and

manipulating the database for various
applications.

3. What is a Database
system?

The database and DBMS software together is
called as Database system.

4. Advantages of DBMS?

Redundancy is controlled. Unauthorised
access is restricted. Providing multiple user interfaces. Enforcing

integrity constraints. Providing backup and recovery.

5. Disadvantage in File
Processing System?

• Data redundancy & inconsistency.

• Difficult in accessing data.

• Data isolation.

• Data integrity.

• Concurrent access is not possible.

• Security Problems.

6. Describe the three
levels of data abstraction?

The are three levels of
abstraction:

1. Physical level: The lowest level of
abstraction describes how data are stored.

2. Logical level: The next higher level of
abstraction, describes what data are stored in database and

what relationship among those
data.

3. View level: The highest level of
abstraction describes only part of entire database.

7. Define the
"Integrity Rules"

There are two Integrity rules.

1. Entity Integrity: States that ?Primary key cannot have NULL value?

2. Referential Integrity: States that ?Foreign Key can be either a NULL value or should be
Primary Key

value of other relation.

8. What is extension and
intension?

Extension - It is the number of tuples present in a table at any instance. This is time
dependent.

Intension - It is a constant value that gives
the name, structure of table and the constraints laid on it.

9. What is System R? What
are its two major subsystems?

System R was designed and developed over a
period of 1974-79 at IBM San Jose Research Center. It is a

prototype and its purpose was to
demonstrate that it is possible to build a Relational System that can be used

in a real life environment
to solve real life problems, with performance at least comparable to that of
existing

system.

Its two subsystems are

• Research Storage

• System Relational Data System.

10. How is the data
structure of System R different from the relational structure?

Unlike Relational systems in System R

• Domains are not supported

• Enforcement of candidate key uniqueness is
optional

• Enforcement of entity integrity is optional

• Referential integrity is not enforced

11. What is Data
Independence?

Data independence means that
?the application is independent of the storage structure and access
strategy

of data?. In other words, The ability to modify the schema definition in one level
should not affect the schema

definition in the next higher level.

Two types of Data Independence are:

1. Physical Data Independence: Modification
in physical level should not affect the logical level.

2. Logical Data Independence: Modification in
logical level should affect the view level.

NOTE: Logical Data Independence is more
difficult to achieve.

12. What is a view? How it
is related to data independence?

A view may be thought of as a virtual table,
that is, a table that does not really exist in its own right but is

instead derived from one or more
underlying base table. In other words, there is no stored file that direct

represents the view instead a
definition of view is stored in data dictionary.

Growth and restructuring of base tables is
not reflected in views. Thus the view can insulate users from the

effects of restructuring and
growth in the database. Hence accounts for logical data independence.

13. What is Data Model?

A collection of conceptual
tools for describing data, data relationships data semantics and constraints.

14. What is E-R model?

E-R model stands for Entity-Relationship
model. This data model is based on real world that consists of basic

objects called entities and of
relationship among these objects. Entities are described in a database by a set

of attributes.

15. What is Object
Oriented model?

This model is based on collection of objects.
An object contains values stored in instance variables with in the

object. An object also contains
bodies of code that operate on the object. These bodies of code are called

methods. Objects that contain
same types of values and the same methods are grouped together into

classes.

16. What is an Entity?

It is a 'thing' in the real world with an
independent existence.

17. What is an Entity
type?

It is a collection (set) of entities that
have same attributes.

18. What is an Entity set?

It is a collection of all entities of
particular entity type in the database.

19. What is an Extension
of entity type?

The collections of entities of a particular
entity type are grouped together into an entity set.

20. What is Weak Entity
set?

An entity set may not have sufficient
attributes to form a primary key, and its primary key compromises of its

partial key and primary key of
its parent entity, then it is said to be Weak Entity set.

21. What is an attribute?

It is a particular property, which describes
the entity.

22. What is a Relation Schema and a Relation?

A relation Schema denoted by R(A1, A2, ?, An) is made up of the relation name R and the
list of attributes Ai

that it contains. A relation
is defined as a set of tuples. Let r be the relation
which contains set tuples (t1, t2,

t3, ..., tn). Each tuple is an ordered
list of n-values t=(v1,v2, ..., vn).

23. What is degree of a
Relation?

It is the number of attribute of its relation
schema.

24. What is Relationship?

It is an association among two or more
entities.

Relationship Set - The collection (or set)
of similar relationships.

Relationship Type - Relationship type
defines a set of associations or a relationship set among a given set

of entity types.

Degree of Relationship
Type - It
is the number of entity type participating.

25. What is DDL (Data Definition
Language)?

A data base schema is specifies by a set of
definitions expressed by a special language called DDL.

26. What is VDL (View
Definition Language)?

It specifies user views and their mappings to
the conceptual schema.

27. What is SDL (Storage
Definition Language)?

This language is to specify the internal
schema. This language may specify the mapping between two

schemas.

28. What is Data Storage -
Definition Language?

The storage structures and access methods
used by database system are specified by a set of definition in a

special type of DDL called data
storage-definition language.

29. What is DML (Data
Manipulation Language)?

This language that enable
user to access or manipulate data as organised by
appropriate data model.

• Procedural DML or Low level: DML requires a
user to specify what data are needed and how to get

those data.

• Non-Procedural DML or High level: DML
requires a user to specify what data are needed without

specifying how to get those data.

30. What is DML Compiler?

It translates DML statements in a query
language into low-level instruction that the query evaluation engine

can understand.

31. What is Query
evaluation engine?

It executes low-level instruction generated
by compiler.

32. What is DDL Interpreter?

It interprets DDL statements and record them in tables containing metadata.

33. What is
Record-at-a-time?

The Low level or Procedural DML can specify
and retrieve each record from a set of records. This retrieve of

a record is said to be
Record-at-a-time.

34. What is Set-at-a-time
or Set-oriented?

The High level or Non-procedural DML can
specify and retrieve many records in a single DML statement.

This retrieve of a record is said to be
Set-at-a-time or Set-oriented.

35. What is Relational
Algebra?

It is procedural query language. It consists
of a set of operations that take one or two relations as input and

produce a new relation.

36. What is Relational
Calculus?

It is an applied predicate calculus
specifically tailored for relational databases proposed by E.F. Codd. E.g. of

languages based on it are DSL
ALPHA, QUEL.

37. How does Tuple-oriented relational calculus differ from
domain-oriented relational calculus?

The tuple-oriented
calculus uses a tuple variables i.e., variable whose
only permitted values are tuples of that

relation. E.g. QUEL

The domain-oriented calculus has domain
variables i.e., variables that range over the underlying domains

instead of over relation. E.g.
ILL, DEDUCE.

38. 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

• Minimizing redundancy

• Minimizing insertion, deletion and update
anomalies.

39. What is Functional
Dependency?

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.

40. When is a functional
dependency F said to be minimal?

• Every dependency in F has a single
attribute for its right hand side.

• It cannot replace any dependency X -->A in F with a dependency Y--> A where Y is a proper
subset of

X and still have a set of dependency that is
equivalent to F.

• We cannot remove any dependency from F and
still have set of dependency that is equivalent to F.

41. What is Multivalued dependency?

Multivalued dependency denoted by
X-->Y specified on relation schema R, where X and Y are both subsets

of R, specifies the
following constraint on any relation r of R: if two tuples
t1 and t2 exist in r such that t1[X] =

t2[X] then t3 and t4 should also exist in r
with the following properties

• t3[x] = t4[X] = t1[X] = t2[X]

• t3[Y] = t1[Y] and t4[Y] = t2[Y]

• t3[Z] = t2[Z] and
t4[Z] = t1[Z]

where [Z = (R-(X U Y)) ]

42. What is Lossless join
property?

It guarantees that the spurious tuple generation does not occur with respect to relation
schemas after

decomposition.

43. What is 1 NF (Normal
Form)?

The domain of attribute must include only
atomic (simple, indivisible) values.

44. What is Fully
Functional dependency?

t 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.

45. 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.

46. 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

• X is a Super-key of R.

• A is a prime attribute of R.

In other words, if every non prime attribute
is non-transitively dependent on primary key.

47. 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.

48. 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

• X is subset or equal to (or) XY = R.

• X is a super key.

49. 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

• Ri = R for some i.

• The join dependency is implied by the set
of FD, over R in which the left side is key of R.

50. What is a Tuple in RDBMS?

A row in a table is called a tuple of the relation. The number of tuples
in a relation is known as the cardinality

of the relation. Tuples in a table are unique and can be arranged in any
order.

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