Dbms Ch1 Doc

7/31/2019 Dbms Ch1 Doc

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Data vs. Information

Data:Raw facts. The word raw indicates that the

facts have not been processed to reveal their

meaning.

Information: Information is produced byprocessing raw data.

Information is then used for decision making.

Good decision making is the key to successful

business, therefore the information produced by

data processing should be accurate, relevant and

timely.

Knowledge: The body of information and facts

about a specific subject is called knowledge.


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Data management: Data management is a

discipline that focuses on proper generation ofdata, storage and retrieval of data.

Database

A database is a shared, integrated computer

structure that stores a collection of:

End user data

Metadata

Metadata is data about the data stored in the

database.

E.g. the name of the field, size, data type,

compulsory field or not etc


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Database Management System

Dbms is a collection of programs that manages

the database structure and controls the access to

data stored in the database.

Dbms serves as an intermediary between the user

and the database.

The dbms receives the data requests from theuser/application program and retrieves the data

from the database and sends it back to the user.

Advantages of the dbms

Improved data Sharing


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Several users can have different views of the

same data. Thus data is shared by all

applications

Better data integration

Data is stored at a centralized location. Data

of the entire organization is stored in the

repository.

Minimized data inconsistency

Multiple versions/copies of the same data are

not stored at different locations hence there is

no redundancy of data. And so there is no

inconsistency.

Improved data access

Data stored in the database can be accessed

easily using queries.

Query is a specific request for data storage,retrieval or modification issued by the user to

the dbms.

Improved decision making


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Better managed data and improved data

access make it possible to generate better

quality information, on which betterdecisions are made.

Increased end user productivity

Quick and good decisions increase the

productivity of the employees and in turn the

success of the organization.

Types of databases

Based on the number of users

Single-user database: supports only one user

at a time


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Desktop database: A single user database that

runs on a personal computer

Multi-user database: supports multiple usersat a time

Workgroup database: multi-user database

that supports less then 50 users or a specific

department in an organization

Enterprise database:when the database is

used by the entire organization and supports

many users, across departments

Based on location

Centralized database: a database that

supports data located at a single location

Distributed database: a database that supportsdata located at multiple locations


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Based on type of use

Operational database: a database that is

designed to support a companys day-to-day

operations is called operational database.

It is also known as transactional orproduction database.

Data warehouse: It stores data which can be

used to generate information that is used fortactical and strategic decision making.

Files and File Systems

Earlier organizations used to keep track of the

necessary data using a manual file system.


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The manual file system consisted of files which

were kept in the filing cabinet.

The content of each file was logically related.

E.g. one file would store data related to the

employee another file would store data related to

the customer, products and so on

As the volume of the data increased and thereporting requirements of the organization

increased the manual file system was difficult to

use.

It was time consuming and complicated.


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There fore the need ofcomputer based system

that would track data and produce reports was

created.

Data processing Specialist: created the

computer file structures to store data, created the

software to manage the file structures, and

designed application programs that producedreports based on the file data.

File Terminology

Data: Raw facts

Character: The smallest piece of data that is

recognized by the computer. It requires one byteof storage.


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Field: A character or group of characters that has

a specific meaning.

Record: A logically related set of one or more

fields that describes a person place thing or an

event.

File:A collection of related records

E.g. a file might contain data about customers or

students etc

Computerized file system saved a lot of time and

effort for the users.

It was quick and easy to search for required

information


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Reports could be generated easily and hence

decision making became better.

So each department started making their own

computerized file system and wrote the

application programs to generate reports.

limitations with File System Data

Management

It requires extensive programming

Simple data retrieval tasks require a lot of

programming effort using 3GL languages.

E.g. COBOL, BASIC, C++ and FORTRAN


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It requires the programmer to code what must

be done and how it must be done.

There are no ad hoc query capabilities

There ad hoc queries become impossible with

3 GL languages. It takes very long to

generate such reports a week or a month etc

System Administration can be complex

System administration becomes difficult as

the number of files in the system goes onincreasing

Difficult to change existing structures

Every file requires its own file managementsystem to add modify and delete records and

to view the contents and generate reports.


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Security features are inadequate

Making changes in the file structure requires

changes to be made in the programs that usedata from that file

Security features are limited. Safeguards

designed to protect confidential data aredifficult to program.

Problems with File System


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The limitations of the file system lead to the

following problems:

Structural and Data dependence

A file system has structural dependence i.e.

access to the file is dependent on its structure.

i.e. if the structure changes the programs

which access the data from the file will also

have to be modified.

Structural Independence exists when it is

possible to make changes in the file structure

without affecting the application programs.


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Data Dependence

Even changes in the file data characteristics

affects the data access programs hence the

file system is said to exhibit data dependence.

E.g. If a field in the file changes from integer

to decimal data type then the program

accessing the data will also requiremodifications.

Data independence exists when it is possible

to make changes in the data storage

characteristics without affecting theapplication programs ability to access data.


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Field Definitions and Naming Conventions

The record and field designs in the file

should take into consideration the reporting

requirements.

E.g. Fname, Lname,City, Area code etc

Field names should be descriptive and

meaningful

Length of the field names should be not too

long and not too short.


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It should convey the name of the file and give

an idea about the kind of data that will be

stored in that field.

E.g. Instead of using REN you can use

CUST_RENEW_DATE

There should be a field which uniquelyidentifies the records in the file.

E.g. CUST_ID

Data Redundancy

The data is stored at multiple locations acrossthe organization.

When there is any modification the data

stored at the different locations may not get

updated consistently, thus creating differentversions of the same data. This is known as

data redundancy.


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Uncontrolled data redundancy creates the

following problems:

Data Inconsistency

Data inconsistency exists when different and

conflicting versions of the same data appearin different places.

Reports generated from such data will also be

incorrect.

The data entry errors are more likely when

the same data has to be entered at many

locations. Spelling mistakes, wrong data etc

Data Anomalies


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Anomaly means an abnormality/mistake.

When data redundancy exists there can be

data anomalies because any change in data atone place requires corresponding

modification at all the locations or in all the

files.

A data anomaly develops when all the

required changes in the redundant data are

not made successfully.

Update Anomalies: If the agents phone nochanges it must be changed for every

customer record who the agent serves.

Insertion anomalies: If only customer data

file exists then to add data about a new a

dummy customer entry must be created.

Deletion anomalies: If you delete a customer

record which is the only record that contains


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a particular agent data, then that agents data

will be lost.

Database Systems

Database consists of logically related data

stored in a single logical data repository.

Physical data format: the format in which

the computer stores the data physically on thestorage device.

Logical data format: the format in which

the users view the data. The users may viewthe same data in a variety of different ways.


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There are multiple logical views of the data.

Database System Environment

Database system consists of hardware,

software, people, procedures and data.

Hardware

Hardware is the physical devices of the

system. E.g. computer, printer, routers,

storage devices etc

Software

Operating system manages all the hardware

and software to work together and run thecomputer.


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Dbms software manages the database within

the database system.

Application programs and utilities help to

access the data from the database and

generate reports and perform other tasks.

People

This component includes all the users of the

database system.

System Administrators: see overall

functioning of the system

Database administrators: also known as

DBA-ensure that the database if functioning

properly

Database designers: database architects,

they design the database structure.


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System analysts and programmers: they

design and implement the application

programs. They create the data entry screens,reports and procedures through which users

can access and manipulate databases data.

End-users: users of the system who use the

application programs.

Procedures

Procedures are the instructions and rules

which govern the design and use of the

database system.It specifies the business rules and standards

for input and output data.

Data

A collection of facts stored in the database.

DBMS Functions


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A DBMS performs several functions to

maintain the integrity and consistency of thedata in the database.

All the functions of the dbms are transparent

to the users i.e. the end-users do know cometo know how the dbms carries out such

functions.

The following functions are performed by

dbms

Data dictionary management

The dbms stores definitions of data elements

and their relationships (metadata) in the datadictionary.


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Whenever a program wants to access the data

it sends the request to the dbms, which then

looks up the required data componentstructures and relationships and relieves the

user the task of programming.

Whenever any changes are made in the

database structure, the changes are updated inthe data dictionary also.

Thus the dbms removes data and structural

dependency from the system.

Data storage management

The dbms creates and manages the complex

structures required for data storage thusrelieving you of the task of programming the

complex physical data characteristics.


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Dbms stores data, data validation rules,

procedural code, images and picture formats

also.

Storage management also does performance

tuning: to make data storage and access more

and more efficient and fast.

Dbms stores data in multiple physical files

and can serve multiple users at a time.

Data transformation and presentation

Dbms does the conversion from physical data

format to logical data format and vice versa

during data retrieval and storage respectively.

Security management


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Dbms creates a security system that enforces

user security and data privacy.

Security rules:

Who can access data?

What can be accessed by whom?

What operations can be performed?

Multi-user access control

Dbms allows multiple users can access the

database concurrently.

Dbms uses complex algorithms to provide

multiple users access to the database without

affecting the data integrity and consistency.

Backup and recovery management


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Dbms provides utilities which allow the

DBAs to perform back up and restore

activities on the database.

Recovery management deals with recovery of

data in case of failure of database.

Back up and recovery is needed to preservethe database integrity.

Data integrity management

Dbms enforces data integrity rules, to

minimize data redundancy.


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The data relationships stored in the data

dictionary are used to enforce data integrity.

Data access languages and application

programming interfaces

Dbms provides data access through a query

language.Query language is a non procedural language

one that lets the user specify what must be

done without specifying how it is to be done.

E.g. SQL

Dbms provides administrative tools to the

dbms and also allows programmers to access

data via procedural languages.

Database communication interfaces


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Users can communicate with the databases in

different ways:

Through the internet using browsers orpublishing reports on the website or through

data entry forms etc

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Dbms Ch1 Doc

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