DBMS Notes
CHAPTER-1
INTRODUCATION TO DBMS
System
A
system is an integration of entities, alternatively designed as components,
which have integration among them.
For E.g.,
consider a particular department in a college (or) university. The entities of
the department are students, non-teaching staff, infrastructure etc. These
entities interact with another.
The information system can be either a
conventional file processing system (or) database management system.
Explain
the Conventional File Processing System:
In the conventional File Processing
System each and every sub system of the information system will have own set of
files. As a result there will be a duplication of data between various sub
systems.
The concept of Conventional File Processing System is shown below.
The above system
consists of 3 sub-systems namely application-x, application-y and applications.
It is clearly that some of the files are
duplicated in different subsystems of the conventional file processing system.
This will intern increase the data redundancy.
Example
of Conventional File Processing System:
The patients come to
the hospital from the society. Upon the arrival of a preliminary registration
is done by seeking information about the patient. Then depending on the type
and illness, the patient will either be treated as out-patient (or) in-patient.
In some cases initially a patient will be treated as out-patient and then the
patient will be admitted as outpatient if necessary. Finally the bills are to
be paid before the patient is discharged. In this system we are using four
files. The files are
Patient File: At the Registration.
In-patient Treatment
File: at the in-patient section.
Out-patient
Treatment File: at the out-patient section.
In Voice File: at
the accounts section.
The files are maintained in different
sections of the hospital in a decentralized manner, certain data items (patient
no, patient name, patient address) will be duplicated. This will have some
undesirable results. Some of the difficulties of the conventional file
processing system of the hospital are the following.
1. There
may be a duplication of data in different sections of the hospital which would
lead to inconsistency of data.
2. A
lot of paper work and telephone calls would be required to synchronize file
structure.
3. The
system cannot provide answer to complex queries.
What
are the Drawbacks of Conventional File Processing System ?
A list of drawbacks
of the Conventional File Processing System is presented below.
1. Uncontrolled
Redundancy of data.
2. Inconsistency
of data.
3. Inflexibility
4. Lack
of backup and recovery
5. Limited
data sharing.
6. Poor
enforcement of standards.
7. Unable
to represent Relationships among data.
8. Excessive
program maintenance and low programming productivity.
1.
Uncontrolled
Redundancy of data
Each sub system of an organization
maintains own set of files without data sharing, the same data will be
available in different files. This will result increased disc space, increased
time of data entry and inconsistency of data.
2.
Inconsistency
of data
The uncontrolled redundancy of data will
permit the system to have the same data in different files. As a result, a
particular data element like patient name will be entered differently in
different files. Which is nothing but inconsistency of that particular data
element . while performing the basic data operations like updation, deletion,
retrieval etc. This inconsistency will give misleading results.
3.
Inflexibility
In
the conventional file processing system generally top down approach will be
followed in file design. In this approach a set of meaningful entities of the
proposed system will be identified along with their attributes to create the
files. The actual set of reports which is required for the system will not be
considered on this approach. As a result , it may not be possible to meet the
requirements of the users fully. Also in the future , if there is a some
changes in the user requirements , then the conventional file processing system
will not be flexible to provide the results.
4.
Lack
of Backup and recovery
In this conventional file processing system
there is no implicit facility for backup and recovery from system failure. It
means that when an application program failed in middle of its work on its
updating on a file.
5.
Limited
data sharing
In the conventional file processing system
the data is stored in a decentralized manner, hence sharing of the data is complex one.
6.
Poor
enforcement of standards
Since different applications and their
respective files were developed by different groups will design data fields,
since each group will follow its own standards for fields name, fields width,
fields type etc. This will create a serious difficulty while modifying programs
and data structures by different groups of users which will leads to low
programmer productivity.
7.
Unable
to represent relationships among data.
In the conventional file processing system
there is no implicit facility to represent relationship among data in different
file for a single system.
8.
Excessive
program maintenance & Low program productivity
Since the different applications are
developed differently by different groups in terms of file specifications and
program specifications, it will be very difficult to modify the programs and
data structure at a later stage by a different group. Many of program variables
may be defined differently in different programs. All these difficulties will
leads to excessive maintenance.
Programmer productivity is a measure of
time taken to develop an application. If the time taken to develop an
application is low then the programmer productivity is high and vice versa.
What
is DATABASE?
Ø Database
is a collection of related data (or) files.
Ø Data
means known facts that can be recorded and that have implicit meaning.
For E.g., consider
the names, telephone numbers and addresses of the people. We have recorded this
data in an address book (or) we may have stored it on a file in the hard disk,
using a computer and software such as Microsoft Excel (or) MS Access. This
collection of inter related data is a database. Generally a database contains
one data file (or) large number of data files. The database is organized in
such a way that a application programs will quickly retrieve the required data.
What
is Database Management System (DBMS)?
A database management system (DBMS) is a
collection of programs that enables users to create and maintain a database.The
DBMS is general-purpose software system that facilitates the defining,
constructing, manipulating and sharing database among various users and
applications.
Defining a
database involves specifying the data types, structures, and constraints for
the data to be stored in the database.
Constructing
the database is the process of storing the data itself on some storage medium
that is controlled by the DBMS.
Manipulating a
database includes such functions as querying the database to retrieve specific
data, updating the database to reflect changes in the database, and generating
reports from the data.
Sharinga
database allows multiple users and programs to access the database
simultaneously. Other important function provided by the DBMS is unauthorized
users cannot access the database.
Example
of Database Management System
Consider
the example of the hospital system which deals in-patients as well as out-
patients. The hospital system is shown below.
In
the Conventional File Processing System there will be a separate system for
in-patients, Out-patient and Accounts. But under the database approach, all the
necessary files are included in a single database, which minimizes redundancy
of data and facilitates sharing. As a result all the drawbacks of Conventional
File Processing System are eliminated in the Database System.
What
are the Advantages of Database Management System:
The Advantages of Database Management System
are
1. Controlled
Redundancy of data.
2. Consistency
of data.
3. Flexibility
4. Backup
and recovery
5. Enhanced
Data sharing.
6. Better
enforcement of standards.
7. Relationships
among data.
8. Reduced
program maintenance and Increased programmer productivity.
1.
Controlled Redundancy of data
The database approach uses a centralized place to save
data hence the amount of data redundancy will be minimized. Data redundancy can
be minimized by applying normalization process in database design.
2.
Consistency of data
The
controlled redundancy will minimize the presence of same data in different
files. This will lead consistency of data by reducing multiple inserts and
updates on same data at different places.
3.
Flexibility
In database
approach , the database design based on bottom up approach. In this approach
all the reports that are currently used and various expected reports are taken
into design the database. When some changes in report requirements occurs
revision of database can be done with minor changes in the database.
4.
Backup and Recovery
In DBMS if a
transaction fails in middle of its execution due to system failure then DBMS
will get back the data into its consistent state as before.
5.
Enhanced Data Sharing
In
database approach uses centralized database hence same data can be shared by
different applications or users simultaneously with concurrency control. In
DBMS multiple users will access same data and can do changes.
6.
Better enforcement of standards
Since different files of the database
are design at a time of a different subsystems, it will be better enforcement
of standards in terms of defining field name, field width , field type etc.,
7.
Relationships among data
We can apply relationships among data
to improve performance of applications and consistency (correctness) of data.
For example foreign key constraint makes a relationship between Employee and
Department information.
8.
Reduced program maintenance and increase of programming productivity.
Different applications are developed
under the coordination of the database administrator. As a result, there will
be a integrated effort among the different group in terms of file design and
program design. This will reduce the program maintenance.
Programmer
productivity is measure of time taken to develop an applications. In database
approach , data is separated from programs. There are many fourth generation
languages available to access and manipulate the database.
Because
of advanced capabilities of fourth generation languages , the time taken to
develop an application will be less when compared to the time taken to develop
using conventional file processing system.
What
are the Application of DBMS ?
The application of database is:
1. Banking:
For customer information, accounts, loans, Bank transactions.
2. Airlines:
For reservations and scheduled information.
3. Universities:
For student information, course registration and grading.
4. Telecommunication:
For keeping records of call mode, generating monthly bills,
maintaining
balances on pre-paid cards and storing information about the communication
Network.
What
are the Disadvantages of DBMS ?
The following are the disadvantages of
using DBMS.
1. Increased
complexity.
2. Requirement
of new and specialized manpower.
3. Large
size of DBMS.
4. Increased
installation and maintenance cast.
5. Conversion
cost.
1.
Increased
complexity
A
multi user DBMS becomes an complex piece of software due to expected
functionalities from it. It becomes necessary for database designers,
developers, database administrator and end users to understand these
functionalities. Failure to understand that can lead to bad designed decisions.
2.
Requirement
of new and specialized manpower
Because
of rapid in database technology and organizations, business need to trained
manpower on regular basis to design and implement of database administrative
services and manage a staff of new people, therefore an organization needs to
maintain specialized skill person.
3.
Large
size of DBMS
The
DBMS occupies many Giga Bytes of storage space and requires more amount of main
memory to run efficiently.
4.
Increased
installation and maintenance cost
The
DBMS software has a high initial cost. It requires trained person to install
and operate. and also has more annual maintenance. Installing such software’s
also requires upgrades to the hardware and software.
5.
Conversion
cost
The
conversion cost from old database technology to modern database environment is
high.
Explain
the DBMS Architecture
1. The
main aim of database system is to provide an abstract view of data hiding of
certain detail of how data is stored. And manipulated, to satisfy these needs
to develop architecture for database system.
2. In
early days the whole DBMS package was a single package where as modern DBMS is
based on client-server architecture.
3. Under
the client-server architecture the database is not present in the client
machine. But the client machine connected to the database system through Network
and server.
4. There
are two types of DBMS architecture as shown below.
In
two-tier architecture, the application is a component that resides on the
client machines that communicate server machine through query language
statements.
In
three-tier architecture, the client machine cannot directly communicate with an
application server, the application server communicates with a database to
access data. Three tier architectures are more suitable for large applications.
Explain
the Database Architecture
A database
Architecture is shown below depending upon the three tier architecture. It
contains of 3 levels.
Internal
level
The
internal schema defines the internal level. The internal level is the lowest
level of data abstraction. This level indicates how the data will be stored
into the database and describes the file structures and data structures and
methods to be used by the data base.
Conceptual
level
The conceptual schema defines the conceptual level. The
conceptual level in the middle level abstraction. This level indicates
entities, attributes, relationship between entities and attributes.
External
level
External schema defines the external level. The external
level is the highest level of data abstraction. This level describes part of
database. i.e., relevant to the user.
What
are the Functions or services of DBMS ?
The functions and services of DBMS are
1.
Data
storage Management
DBMS creates the structure for database
in the physical storage devices. It provides a mechanism for permanent storage
of dat.
2.
Data
Manipulation Management
The DBMS provides ability to add new data into the database (or)
retrieve, update and delete existing data in the database.
3.
Data
Definition Management
The DBMS creates the structure of data
in which the data is stored.
4.
Data
dictionary
The DBMS provides a data dictionary in
which stores the description of data items.
5.
Authorization
The DBMS protects the database against unauthorized access either
intentional (or) accidental.
6.
Backup
and recovery
The DBMS provides a mechanism for Backup data periodically and recovery
from different types of failures.
7.
Concurrency
control
The DBMS supports sharing of data among
multiple users. The DBMS provides a mechanism for concurrent access to the
database.
8.
Transaction
Management
The transaction in a series of database
operations, which access (or) changes the content of the database. This is done
by the transaction management.
9.
Data
Independency Service
The DBMS supports the independency of
the programs from its structure of the database.
10.
Integrity
Service
The DBMS provides
integrity service to store the data into the database (or) to change the data
into the database follows certain rules.
What
are the Functions database Administrator ?
Database administrator is an
individual person with an overview of one (or) more databases and also controls
the design and use of database.
Functions and responsibilities of DBA
are
1.
Defining
conceptual schema and database creation
The DBA creates the
conceptual schema such as defining entities and attributes, deleting entities
and attributes and modifying entities and attributes etc. The DBA also creates
the structure of the database.
2.
storage
structure and access method definition
The DBA defines the
storage structure of the data. And access methods of the database.
3.
Granting
authorization to the user
The DBA grants the
access to use the database to its users. The authorization information is kept
is a system, the database system consults whenever someone attempt to access
the data in the system.
4.
Routine
maintenance
The DBA maintains
periodically backups of the database either on hard disc (or) CD to prevent
loss of data in case of failure.
5.
Job
monitoring
The DBA is
responsible for the performance of data is not decreased.
What
are the various components of Database Systems
?
The database system is composed of the five major components.
1.
Hardware
2.
Software
3.
People
4.
Producers
5.
Data
1.
Hardware:
Hardware refers to physical components of the system.
E.g. storage
devices, printers etc.
2.
Software:
software
is a set of programs. To make database system function fully, three types of
software’s are needed. They are
a. Operating System Software
b. DBMS software.
c. Application Programs and utility software.
a. Operating system software: operating system manages all hardware
components and run other software’s on the computer.
E.g. WINDOWS, LINUX
b. DBMS Software: manages the
database within the database system.
E.g. Oracle, SQL, MS Access
C. Application programs and utility software: Application programs are used to access
and manipulate data to generate reports and making decisions.
Utilities are the software tools used to help, manage
the database systems computer components.
3.
People:
There
are five types of users in the database system.
a.
System
Administrator: to see the database systems general
operation.
b.
Database
Administrator: see the database is functionality properly.
c.
Database
designers: design the database structure.
d.
System
analyst and programmers: Design and implement the application
programs.
e.
End
user: use the application programs to run the organization
daily operations.
4.
Procedures: procedures are the set of rules based on
design and use the database.
5.
Data: The data is a facts stored in the database.
Because data are the raw material from which the information is generated.
What is Data?
A system consists of interrelated entities,
each entity has a set of attributes of entities of the system.
What is Information ?
Information is nothing but processed
data.
Define Meta data
Meta data is the data about the data
i.e., information for accessing the data.
Explain the Terminology of
a file
Field: A
field is the lowest level of data item of an entity which is alternatively
called as an attribute of that entity.
Emp Empno Empname Empaddress
Record: Record
is the collection of fields (or) attributes of an entity.
Empno Empname Empaddress
1 sweaty banglore
File: File is a
collection of records having same set of fields arranged in the same sequence.
Empno Empname Empaddress
1 manimala Chennai
2 priya Hyderabad
Key field (or) Primary key: A
key field is said to be key field (Or) primary key if it can identify a record
uniquely in a file.
e.g. student no in student file
emp no in emp file.
Non key field (or) secondary key: A
field is said to be Non key field (or) secondary key if it cannot identify a
record uniquely in a file.
e.g. student name in student file.
Emp name in emp file.
Schema: it
is a overall view of all the files in the database.
Subschema: A
portion of the schema of a database is called as subschema.
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