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Introduction to Data Base Management System
(DBMS)
As the name suggests, the database management system consists of two parts
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Database and
2
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Data: Facts, figures, statistics etc
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g
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Record: Collection of related data items, e
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in the above example the three data items had no
meaning
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Roll
Name
Age
1
ABC
19
Table or Relation: Collection of related records
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The rows are called
Tuples or Records
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Consider the following collection of tables:
T1
Roll
Name
Age
1
ABC
19
2
DEF
22
3
XYZ
28
T2
Roll
Address
1
KOL
2
DEL
3
MUM
T3
Roll
Year
1
I
2
II
3
I

T4
Year
Hostel
I
H1
II
H2
We now have a collection of 4 tables
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Because of these common attributes we may combine the data of two or more tables together to
find out the complete details of a student
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In a database, data is organized strictly in row and column format
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The data items within one row may belong to different data types
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All the data items within a single attribute are
of the same data type
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It also helps us to add, modify delete data items in the database
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The management system is important because without the existence of some kind of rules and
regulations it is not possible to maintain the database
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These issues must be resolved by having some kind of rules to follow in order to
maintain the integrity of the database
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Likewise, the database that we have created already can have different aspects to reveal if seen
from different levels of abstraction
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Generally it
means the amount of detail you want to hide
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Let us illustrate by
a simple example
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We do not know
what parts it is built with
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If we open the computer case and look inside at the hard disc, motherboard, CD drive,
CPU and RAM, we are in middle level of abstraction
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In the same manner, the database can also be viewed from different levels of abstraction to reveal
different levels of details
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We discuss them here
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The diagram above shows the three different schemas used in DBMS, seen from different levels
of abstraction
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) are stored in the physical storage (Hard Disc, CD, Tape
Drive etc
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This schema
is useful for database application developers and database administrator
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Please note that at this level we are not interested with the raw data items
anymore, we are interested with the structure of the database
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Conceptual
or Logical schema is very useful for database administrators whose responsibility is to maintain
the entire database
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This is targeted for the end
users
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We may not want the end
user to become confused with astounding amount of details by allowing him/her to have a look at

the entire database, or we may also not allow this for the purpose of security, where sensitive
information must remain hidden from unwanted persons
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These
tables are also known as virtual tables, because they have no separate physical existence
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Say for example, in our sample database we have
created earlier, we have a special officer whose responsibility is to keep in touch with the parents
of any under aged student living in the hostels
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The database administrator may create a virtual table
with only these four attributes, only for the use of this officer
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It is the property of the database which tries
to ensure that if we make any change in any level of schema of the database, the schema
immediately above it would require minimal or no need of change
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If we
change the design of any one floor, e
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extending the width of a room by demolishing the
western wall of that room, it is likely that the design in the above floors will have to be changed
also
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Would not life be easy if the change could be contained in one floor only? Data independence is
the answer for this
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Data independence can be classified into the following two types:
1
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This is practically easier to
achieve
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Say, you have bought an Audio CD of a recently released film and one of your friends has
bought an Audio Cassette of the same film
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The first is digital recording on an optical media, where random access is possible
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However, how
this change is reflected in the logical schema is very interesting
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We have
information like Track no, Name of the Song, Name of the Artist and Duration of the Track,
things which are identical for both the CD and the Cassette
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2
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As we shall see, this is a little
difficult to achieve
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Suppose the CD you have bought contains 6 songs, and some of your friends are interested in
copying some of those songs (which they like in the film) into their favorite collection
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Each of

these collections can be compared to a view schema for that friend
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Obviously, you will have to
ask the friends who have song 3 in their proposed collection to alter their view by deleting song 3
from their proposed collection as well
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S/he has the flowing
functions and responsibilities regarding database management:
1
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2
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3
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e
...
e
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4
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DBA is responsible to create user roles, which are collection of
the permissions (like read, write etc
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S/he can
also grant additional permissions to and/or revoke existing permissions from a user if
need be
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Defining the integrity constraints for the database to ensure that the data entered conform

to some rules, thereby increasing the reliability of data
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Creating a security mechanism to prevent unauthorized access, accidental or intentional

handling of data that can cause security threat
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Creating backup and recovery policy
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It is essential to keep regular backup of the data so that
if the system fails then all data up to the point of failure will be available from a stable
storage
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Advantages and Disadvantages of Database Management System
We must evaluate whether there is any gain in using a DBMS over a situation where we do not
use it
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1
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Redundancy is the problem of storing the same data item in more one place
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Anomalies may occur in the database if insertion, deletion etc are not
done properly
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Sharing of Data: In a paper-based record keeping, data cannot be shared among many

users
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3
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This increases the reliability of the database as it can be guaranteed that no
wrong data can exist within the database at any point of time
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Data security: We can restrict certain people from accessing the database or allow them

to see certain portion of the database while blocking sensitive information
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However, there could be a few disadvantages of using DBMS
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As DBMS needs computers, we have to invest a good amount in acquiring the hardware,

software, installation facilities and training of users
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We have to keep regular backups because a failure can occur any time
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3
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If someone

can bypass the security system then the database would become open to any kind of
mishandling

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