Relational database management system (rdbms) i

Objective
 Objective of this lecture is to make students be able to
understand the basic concepts of file system and
database.
 To introduce the problems with traditional file system
and advantages of database over file system.

Index
 What is file System?
 Characteristics of file system
 Traditional method of data storage
 Problems with Traditional approach
 What is database and DBMS?
 Advantages of DBMS
 Difference between file system and database

File System
 File system was an early attempt to computerize the
manual filing system.
 A file system is a method for storing and organizing
computer files and the data to make it easy to find and
access.
 File Systems may use a storage device such as a hard
disk or CD-ROM.

Characteristics of File Processing System
 It is group of files storing data of an organization.
 Each file is independent from one another.
 Each file is called flat file.
 Each file contained and processed information for one
specific function like accounting or inventory.
 Files are designed by using application programs written
in programming languages such as COBOL, C, C++, etc….

Flat file
 A flat file is a file containing records that have no
structured interrelationship

Traditional Method of Data Storage

Problems: Traditional approach
 Data Security
 Data Redundancy
 Data Isolation
 Program/ Data Dependence
 Concurrent Access Anomalies

Data Security
 The data as maintained in flat files is easily accessible
and therefore not secure.
 Example: the Customer_Transaction file has details
about the total available balance of all customers.
 A customer wants information about his/her account
balance.
 In a file system it is difficult to give the customer access
to only his/her data in the file.
 Thus enforcing security constraints for entire file or for
certain data items are difficult.

Data Redundancy
 Often the same information is duplicated in two or
more files.
 It may lead to inconsistency
 Assume the same data is repeated in two or more files.
If change is made to data in one file, it is required that
change be made to the data in the other file as well.
 If this is not done, it will lead to multiple different
values for same data field.

Relational database management system (rdbms) i

Data Isolation
 Data isolation means that all the related data is not
available in one file.
 Generally, the data scattered in various files, and the
files may be in different formats, therefore writing new
application programs to retrieve the appropriate data
is difficult.

Program/ Data Dependence
 Assume in a banking system there is need to find out
the names of all customers who live within a particular
postal-code area.
 But there is only a program to generate the list of all
customers.
 The bank officer has now two choices: either obtain
the list of all customers and extract the needed
information manually or ask a system programmer to
write the necessary application program.
 Both the alternatives are obviously unsatisfactory.

Concurrent Access Anomalies
 Many systems allow multiple users to update the data
simultaneously. In such environment, interaction of
concurrent updates may result in inconsistent data.
 Example: Bank account A containing Rs. 6000/-. If two
transactions of withdraw funds( Rs 500/- and Rs 1000/-
respectively) from account about same time, result of the
concurrent executions may leave the account in an
incorrect state.
 Program on the behalf of each withdrawal read the old
balance, reduce amount and write result back.
 If both two programs are concurrent they both may read
the value Rs 6000/-.
 Depending on which one writes the value last, the account
may contain either Rs 5500/- or Rs 5000/-, rather than the
correct value of Rs 4500/-

Database Approach
 In order to remove all the above limitations of the File
Based Approach, a new approach was required that
must be more effective known as Database approach.
 A database is a computer based record keeping system
whose over all purpose is to record and maintain
information.
 The database is a single, large repository of data, which
can be used simultaneously by many departments and
users.

The Database Management System (DBMS)

 DBMS A database management system is the software system that
allows users to define, create and maintain a database and provides
controlled access to the data.
 A database management system (DBMS) is basically a collection of
programs that enables users to store, modify, and extract information
from a database as per the requirements.
 DBMS is an intermediate layer between programs and the data.
Programs access the DBMS, which then accesses the data.
 The following are main examples of database applications:
 Banking System
 College Management System
 Inventory Control System
 Hospital Management

Programming Languages
4GL ( Database Query
Languages, Data
Manipulation, analysis and
Reporting Languages)

High-Level Languages

Assembly Language

Machine Language

Difference Between File and DBMS Operations

Advantages of DBMS
 Controlling redundancy
 Enforces integrity constraints
 Better security
 Better flexibility
 Effective data sharing
 Enables backup and recovery

Controlling Redundancy
 Redundant Data

Non-Redundant Database
 In case of centralized database, data can be shared
by number of applications and whole college can
maintain its data with the following database:

Every application can access the information of other’s by
joining on the basis of column ( Rollno )

Enforcing Integrity Constraints
 Integrity of data means that data in database is always accurate.
 Integrity constraints are enforced on database.
 Example: Let us consider the case of college database and
suppose that college having only Btech, Mtech, MCA, MSc, BCA,
BBA and Bcom. But if a user enters the class MS, then incorrect
information must not be stored in database and must be
prompted that this is an invalid entry. Integrity is to be enforced
on class attribute.
 In file system this constraint must be enforced an all the
application separately.
 In case of DBMS this integrity constraint is applied only once on
the class field of the General Office.

How to enforce integrity?
 Integrity rules:
 Entity Integrity rule: Primary key value should not be
null (Mandatory field)
 Referential Integrity: The values of foreign key should
match the primary key in parent table.

Solution to concurrency Anomaly
S (Shared Lock) X (Exclusive Lock)

S true false

X false false

Locks
T1 T2
• Lock-X(B);
• Read(B,b); • Lock-S(A);
• b:=b-50; • Read(A,a);
• Write(B,b); • Unlock(A);
• Unlock(B); • Lock-S(B)
• Lock-X(A); • Read(B,b);
• Read(A,a); • Unlock(B);
• a:=a+50; • Display(a+b);
• Write(A,a)
• Unlock(A);

Schedule 1
T1 T2 Concurrency-control manager
• Lock-X(B); • Grant-X(B,T1)
• Read(B,b);
• b:=b-50;
• Write(B,b)
• Unlock(B)
• Lock-S(A); • Grant-S(A,T2)
• Read(A,a);
• Unlock(A);
• Lock-S(B) • Grant-S(B,T2)
• Read(B,b);
• Unlock(B);
• Display(a+b);
• Grant-X(A,T2)
• Lock-X(A)
• Read(A,a)
• a:=a+50;
• Write(A,a)
• Unlock(A);

Difference between file system and DBMS

Relational database management system (rdbms) i

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