database concept

DATABASE CONCEPT

Database can be defined as a collection

of information organized in such a way that

it can be accessed easily.

Examples of database:

i. Telephone directory

ii. Tracking customer orders

iii. Maintain employees records.

Database Terminologies Data

This is the fact, or about specific entity(person,place or thing) Information

Is the data that have been processed and is useful to the user Field

Is a single item of information or data in entity

e.g. employee name Record

Is a group of fields about an entity,example

Employee’s particulars

USER

FILE KEEPER

FILE CABINET

MANUAL FILE SYSTEM

FILE PROCESSING SYSTEM Information stored as group of records in

separate filesFile systems consisted of a few data files and

many application programsEach file called a soft fileFlat file contained the processed information

for one specific functionUse of programming languages to write

applications

File processing systems structure

Customer fileCustomer file

User 1

Rental fileRental file

User 2

CustomerProcessing Application

CustomerProcessing Application

Rental ProcessingApplication

Rental ProcessingApplication

Rental fileRental file

Customer file

Limitation of File Processing system

i. Separate and isolated data To make decision, user might need data from more than one fileii. Data redundancy often the same information was stored in more than

one file, in addition to taking up more space in the system, this cause loss of data integrity

iii. Program data independence for file formats and access

techniques

iv. Difficult in representing data from user’s view

To create useful application for user, often data from various files must be combined. In file processing system, it was difficult to determine the relationship between isolated data in order to meet user requirement.

v. Data inflexibility

Program-data independency and data isolation limited the flexibility of the file processing system in providing user requirement

Due to this limitations, the concept of

Data base management system (DBMS) was born

DATA BASE MANAGEMENT SYSTEM(DBMS)

Is a program that allows users to define, create, manipulate, store, maintain retrieve and process the data in the data base in order to produce meaningful information.

Focus on information presentation Data stored as a records in various database files that can

be combined to produce meaningful information for users It controls all functions of capturing, processing, storing,

retrieving data and generates various forms of data output Manage access by multiple users and multiple programs to

common stored data. And hence it overcomes all limitations of FPS

DBMS STRUCTURE

USER 1USER 1

USER 2USER 2

USER 3USER 3

RPARPA

OPAOPA

DBMSDBMSDATABASEDATABASE

CPA

CHARACTERISTICS OF DMS

i. Computerized record keeping system

ii. Contain facilities that allow user to:

(a)add, and delete files

(b)Insert,retrieve, update, delete data

iii. Collection of databases; each can be used for separate purposes or combined

EXAMPLES OF DBMSMs ACCESSSQL SERVERORACLEMY SQL

FUNCTIONS OF DBMSTo store dataTo organize dataTo control access to dataTo protect data

USES OF DBMSTo provide decision supportTo provide transaction processing

COMPONENTS OF DBMSThe basic components of a DBMS can be

divided into three subsystemi. Design tool This provide features for creating the

data base and various application, forms, and reports

ii. Run-time facilities This process the application created by design tools.iii. DBMS engine Translates between the design tools

and run time facilities and data

ADVANTAGES OF DBMSi. Centralized data reduce management

problems

ii. Data redundancy and consistency are controllable

iii. Program-data interdependence is diminished

iv. Flexibility of data is increased

DISADVANTAGES OF DBMS

i. Reduction in speed of data access time

ii. Require special knowledge

iii. Possible dependency of application programs to specific DBMS versions

DATABASE ADMINISTRTATOR

Is a one who controls and manage the data base

Functions of DBMSTo make decisions concerns the content of

the data basePlan storage strictures and access

strategies.Provide user supportTo define security and integrity checks Interpret backup and recovery strategies

FLAT DATABASE MODEL

The earliest and simplest database model Is a way of organizing information in a

single tableIs good only for simple databasePossible redundancy of data

HIERARCHICAL DATABASE MODEL

As its name implies, the hierarchical database model defines hierarchically arrangement of data

Is like upside down tree A single table acts as a root of the database from

which the other table branches outRelationship in such system are thought of in

terms of children an parents, such as a children may have only one parent but a parent can have multiple children

Parents and children are tied together by links called “pointers”

More efficient than Flat databaseHas some serious problems, that you can not add a

record to a child table until it has already been incorporated with the parent

Redundancy of data may occur because it does not handle many to may relationship

NETWORK DATABASE MODEL

It was designed to solve problems of hierarchical data base model

It solves the problem of data redundancy by representing relationship in terms of sets rather than hierarchy

It is similar to the hierarchical model, in fact the hierarchy model is a subset of network model

But this model was difficult to implement, so another simple model was developed, which is RELATIONAL DATABASE MODEL

RELATIONAL DATABASE MODEL Is a collection of data items organized as a set of

formally-describes tables from which data can be accessed or reassembled in many different ways without having to reorganize the data base tables

A collection of data organized in two-dimensional tables consisting of named columns and rows

It is easy to create It is easy to extend, after original database creation. The core of Relational data base model is the concept

of table, which is also called relation in which all data is stored

Each table is made up of records (horizontal rows also known as tuples) and fields (vertical column also known as attributes)

Table-is a two dimensional representation of data consisting of column and zero or more rows*

The table name must be uniqueThe table name must be descriptiveColumn name must be unique within the

table, however those columns in different tables my share the same name

Rows must be unique

Null values-is a missing or unknown value in a column of a table, null are not the same as zeros

Primary key-is the column or group of columns whose values uniquely identify each row of a table

Every table must have only one PKPk must always have a valuePK must be uniqueForeign key is a column or group of columns

that is a primary key in another table, it relates the rows of the table to other rows that appear elsewhere in another table

DATABASE DEVELOPMENTThe process can be broken into 5 phases (i)Planning (ii)Analysis (iii)Design (iv)Implementation (v)MaintenanceThese phases often overlap, and some

techniques and tools may be used in more than one stage, especially between analysis and design. E.g Data Dictionary

Data base design is non deterministic

PLANING PHASEHere the overall database structure is defined.It involves the following tasks

1. The purpose of database is determinedWhat information will be usedHow information is to be useWhat question will be answered

2. Feasibility study are conducted

3. Requirements are gathered

Analysis phaseDatabase can be analyzed on different models:

i. Conceptual model

ii. Logical model

iii. Physical model

Conceptual model It provide the framework for developing a

database structure schema from top to down Three data base components (entities,attributes

an relationship) are described in detail.

EntitiesThis defines a thing that exist and is

distinguishable from which data will be collected, e.g person,place or object.

These are are basic building blocks of database Entity instanceIs a particular occurrence of an entityEntity set/class/typeA group of similar entitiesAttributesThis describes the properties of entities and relationship

Relationship

A relationship is a connection between entity classes.

Example, relationship between PERSONS

and AUTOMOBILES could be an “OWNS”

That is to say , people own automobileTypes of relationship

We have three types of relationship

1.one-to-one

2. One-to-may

3.Many-to-manyCandidate keys

Logical modelThis is done after conceptual modelTables and fields are extractedEntities modeled as tablesAttributes modeled as fieldsEach entity instance is called a record.PK and FK are determinedAfter that Normalization process takes place

Physical modelThis defines how data will be stored and

accessed in a computer system

DESIGN PHASEThis determines how best the information system

that was obtained

The following should be determined and

and represented in design phaseTables neededFields needed for each tableRelationships between tablesDBMSUser views (Input forms, output reports)Security mechanism

April 11, 2023 AT(CIT, Kili Com.net) DBMS 32

Database Management Systems (DBMS)

Aiwinia TembaComputing and Information Technology Dept.

Kili Com.net

&

Aiwindory.inc


Course Co-ordinator

Aiwinia [email protected]

Address:Boma Road Opposite Immigration Office,Address:Boma Road Opposite Immigration Office,

P.O BOX 7797 Moshi -Tanzania

Website: www.kilicom.netConsultation HoursMonday & Friday

09:00 AM-16:00PM

mailto:[email protected]


An Integrated of :-

• Introduction– Fundamentals of database– File Processing

• Database processing• Common database software• Database Management Systems (DBMS)• Relational Database Management Systems (RDBMS)• Data Normalization• Introduction to Structured Query Language (SQL)• Implementation of a Relational Database using a RDBMS


Recommended Readings• Leon, A. and Leon,M (2002) Database Management

Systems,Dar es Salaam University Press• Narang, Rajesh (2004) Database Management Systems,

New Delhi• David Kroenke (2002), Database Processing:

Fundamentals, Design and Implementation, 8th Edition, Prentice Hall, Upper Saddle River NJ

• Thomas M. Connolly and Carolyn E. Begg (2002), Database Systems: A Practical Approach to Design, Implementation, and Management, 3rd Edition, Addison-Wesley, Harlow England. – Note, Additional Readings shall be provided if necessary.


Outline–Fundamentals of Database–File Processing–Advantages & Disadvantages of File Process Approach–Data Processing–Data Management–Data Independence–Data Administration Roles


Fundamentals of Database

• Computer uses databases by using a set of well defined rules.

• Example, Assume that each card in the mailbox has five lines of data items, namely as:-– Name, Locality, City, State and Pin_Code– These fields combined to form a record.– Generally, A database contains the following.

• Field• Record• File• Database • Key Field


Fundamentals of Database…….Name

Fields Or

Data Items

Record

StateCityLocality Pin_Code

Abdallah 9 Beveridge Street Manchester UK 110059

1. Abdallah 9 Beveridge Street Manchester UK 110059

Record # Name Locality City State Pin_Code

Field Name

2. Gauravaz 12/B Mohan Garden Mombai MH 400003

3. Deepak WZ-92 Palam Vihar Leeds UK 320001

4. Fazal 121. Pankha Rd New Delhi ND 110045

Record (1st)

Record (4th)

Field |Contents

Figure 1 Illustrates the concepts of Fields, Records, and Files


Fundamentals of Database…….

• Field – The smallest piece of meaningful information

in a file is called a data item or Field.– A data item is generally used for a group of

alphanumeric characters.– Example, Name, Locality, City, State,

Pin_Code are all known as Data Items or Fields as shown in figure 1


Fundamentals of Database…….• Record

– Collection of related fields– Example, Figure 1 contains four records and each

record has five related fields namely as• Name, Locality, City, State and Pin_Code

• File– Is the Collection of all related records. – Example, in figure 1, the file contains the list of

addresses of four friends.


Fundamentals of Database…….

Emp_Code Emp_CodeAddress Salary Emp_Code Name

Recordsà Contain Related

Fields

File 1Contains 100 Records of Empl.



------ ------ ------

Filesà Contain Related

Records

Relating Key Fields

Records of 100 Employees



File 3File 2File 1

Databaseà Contain Related

Files

Fields

Field 1 Field 2 Field 2Field 1 Field 1 Field 2

Figure 2 illustrates the concepts of Fields, Records, Files and Database


Fundamentals of Database…….• Database

– Database is a collection of related files.

– A database is an organised collection of facts

– Is a Collection of information arranged and presented to serve an assigned purpose

– Examples-• A dictionary, where words are arranged alphabetically

• Telephone directory where subscriber names are listed in alphabetic order.

• Figure 2 shows Employees Database having related files containing records of employees


Fundamentals of Database…….• Key Field

– The Keyfield in a record is a unique data item which is used to identify the record for the purpose of accessing and manipulating database

– In figure 2, • File 1 contains employee records with fields Emp_Code and

Address, • File 2 contains employee records with fields Emp_Code and

Salary• File 3 contains employee records with fields Emp_Code and

Name• All the three files have one common field, namely

Emp_Code, this field is called the Keyfield – Is used for identifying and relating records


File Processing

• Data, Information, Knowledge


File Processing……….• Data

– Are raw facts which can be manipulated– Data is required in the operation of any organisation and the same

or similar data may be required for various purposes

• Information– The manipulation of data, simply information is summarization of

data in presentable form– Data consists of facts which become information when they are

processed and convey meaning to people.– Information is the backbone of any organisation – Information is the critical factor that enables managers and

organisations to gain a competitive advantage. It can be considered as the most critical resource of an organisation.


File Processing……….

• Information………..– It is the indispensable link that ties together all

the components of an organisation for better operation and coordination and for survival in today’s brutally competitive environment.

Definition,Information is ‘data that have been put into a meaningful and useful context and communicated to a recipient who uses it to make decision’ (Burch and Grudnitski,1989)



• Information…….– It involves the communication and recipient of

intelligence or knowledge

– It should predict the future with reasonable level of accuracy

– It should help the managers make the best decision and a prevent them from taking wrong decision

– It consists of data , images , text , documents and voice often inextricably intertwined but always organised in a meaningful context.



• Information……..– Notice that the data that is being processed or refined

can be input, stored or both and this formulates the cycle of information, refer figure 3.

– Example, If orders and payments are data, then balance_due and quantity_in_hand would be the information

• Knowledge – Refers to as the facts , events and inference rules used

by a computer program in order to operate intelligently.– It refers to a person’s capability and wisdom as how

much that person knows about one particular subject


File Processing……….Input

(Data)Process(Models)

Output(Information)

Database

DataCaptured

Results Action Decision

Figure 3, Information Cycle


File Processing……….• Information Processing

– Information processing is the acquisition, storage, organisation retrieval, display and dissemination of information

– Quality information means that the information that is

– Accurate

– Timely

– Relevant



• Files, File organisation and Management• File

– A file is a collection of bytes stored as an individual entity

– All data on disk is stored as a file with an assigned file name that is unique within the directory it resides it.

– To the computer, a file is the series of bytes– The structure of a file is known to the software that

manipulate it.


File Processing……….• File…..

– It contains data that is needed for information processing

– These data is called entities, An entity is anything about which information can be stored, examples, physical object, a person, concept or event and so on

– An attribute is a characteristic of interest about an entity.



• File……..– The values of the attributes describe a particular

entity.– An Instance of the entity is represented by a set

of specific values for each of the attributesExamples,

Entity – a boda boda

Attributes (boda) –Make, Model, Price, Eng. Capacity

Instances (boda) –Boda boda, Tsh1000000, £12,000,



• File………..– In data storage, data items are usually grouped

together to describe an entity

• There are different types of files, – Master files– Transaction files– Report files


File Processing……….• Master files

– A file of relatively permanent information about entities

– These files are used as a source of reference data for processing transactions and accumulated information based on the transaction data.

– Example, the accounts master file in a bank will contain details like account name, balance, address and so on



• Transaction Files– A collection of records describing activities or

transactions by organisation.– Created as a result of transactions and preparing

transaction documents– Are used to update the details in the master file– Example in the same bank system, the day-to-

day activities like money withdrawals, deposits and transfers.



• Report Files– A file created by extracting data to prepare a

report– Example, All accounts sorted by account

number containing the details like account name, balance and so on



• Operations on Files– There are mainly two kinds of file operations

• Retrieval and• Update operations

– Retrieval operations do not change the contents of the file thus it only locates records in the file matching certain specific criteria

– Update operations change the contents of the file by modifying the records, deleting (delete) the records and inserting (Insert) new records



• Operations on Files……– The following five operations are required for

the processing of records in files• File creation

• Records location

• Record creation

• Record deletion

• Record modification


File Processing……….• File Organisation

– A technique for physically arranging the records of a file on secondary storage devices

– Factors necessary to be considered when choosing the file organisation

• Speed of data retrieval• Speed of processing data• Speed of update operations• Storage space• Security


File Processing……….• File organisation…..

– Two types of file organisation are • Sequential file organisation and • Direct file organisation

– Sequential file organisation• Records are stored in some predetermined sequence one

after the other• It contains one field referred to as Primary Key• Primary Key usually determines their sequence or

order



• Sequential file organisation….– A primary key is a field ( or set of fields) whose

contents is unique to one record and can therefore be used to identify that record.

– Example, Student_ID, Customer_ID, Emp_ID and so on

– Sequential file organisation is very common because it makes effective use of the least expensive secondary storage device –the magnetic tape

April 11, 2023 AS(CIT, IFM) DBMS 63


• Sequential file organisation….– Records must be processed and accessed

sequentially– It means when using sequential access to reach a

particular record, all records preceding it most first be processed

– Efficient when the entire file or an appreciable portion of the file must be processed together

– Processing data using sequential access referred to as sequential file processing


File Processing……….• Advantages of Sequential file processing

– It uses magnetic tape, the least expensive method of secondary storage.

– It is the most efficient form of organisation when the entire of file or most of it is processed at once

– Transaction file and old master file together act as a back-up, it can be used to create the new master file when existing one damaged or destroyed



• Disadvantages ..– Time factor –the time it takes to access a

particular record may be too long for many applications

– The entire file most be accessed and a new master file created , even if only one record requires maintenance or updating.

04/11/23 DBMS AT(CIT, Kili Com.net) 66

File Processing……….• Advantages of Sequential file processing

– It uses magnetic tape, the least expensive method of secondary storage.

– It is the most efficient form of organisation when the entire of file or most of it is processed at once

– Transaction file and old master file together act as a back-up, it can be used to create the new master file when existing one damaged or destroyed



• Disadvantages ..– Time factor –the time it takes to access a

particular record may be too long for many applications

– The entire file most be accessed and a new master file created , even if only one record requires maintenance or updating.



• Direct File Organisation– The data can be organised in such a way that they are

scattered throughout the disk

– This form of organisation that supports direct access also referred to as random access

– The records can be accessed nearly instantaneously and in any order

– When a record accessed, a record can be read or updated and when this process competed , then the system is free to respond to another request



• Direct processing requires either magnetic disk or optical disk and cannot use magnetic tape

• Direct access systems do not search the entire file rather, they move direct or nearly directly to the required record, to do this the system must have some way to determine where a particular record is stored

• Example, in figure 4, data are entered directly into the system through a terminal that is in contact with the CPU of the central computer, the system locates the specific record in the master file and then updates it.



`

TerminalCPU

1 U

Direct Access Storage Device (DASD)

Figure 4, Direct File Processing –Records are accessed directly



• Direct file processing….– There are several strategies which are used to find record..

• Relative addressing• Hashing (randomising)• Indexing

• Relative addressing– Simplest method of finding a record– A record’s primary key is associated with a specific physical

storage location– On retrieval process, the user enters the Key and the disk

operating system associates this key with the appropriate location on the disk



• Relative addressing….– Relative addressing loses its appeal when the record key

cannot be made to match the physical location

• Hashing also known as Randomising– Method for determining the physical location of a record.– The record key is processed mathematically and another

number is computed that represents the location where the record will be stored

– Record keys are transformed into storage addresses and by using an arithmetic procedures called randomising or hashing algorithm


File Processing……….– The task of this process is to take a set of records keys and find

a formula to map them into set of disk storage location Identifiers

– On retrieval process, user needs to retrieve the record once its key is entered and the hashing routine is used to determine where the record can be found on storage disks.

– Major difficulty with the hashing procedure is due to that some addresses will never get generated whilst two or more record keys produce identical disk address or synonyms or Collisions



• Indexing – It uses a primary index which associates a primary key with

the physical location in which a record is stored.

• Advantages of direct file organisation– Data can be accessed directly and quickly– Primary and secondary indexes can be used to search data in

many ways– Files can still be processed sequentially using secondary

index – Centrally maintained data can be kept up-date

04/11/23 DBMS AS(CIT,IFM) 75


• Disadvantages of direct file processing– The use of an index lowers the computer

system’s efficiency– The hardware must be expensive for these

systems because all data must be stored on disks– There will be no backup data if a file destroyed,

the files are updated directly and no transaction files are maintained on system


File Processing……….• Summary on direct file organisation

– The choice of file organisation and the methods used for direct access depend on the five characteristics

• File volatility

• File activity

• File query needs

• File size

• Data currency


Data Processing

• Data processing comprises the following;– Capturing of data

– Storing of data

– Updating and retrieving of data and information

• Data Management– Data management is the arrangement of all data and

information with an organization

– It also refers to the methods of physical storage and retrieval of data on a disk or other storage devices


Data Management..

• Data management involves the following,– Data administration– The standards of defining data – The way in which people perceive and use data

in their day-to-day activities


Data Independence

• Data Independence– Data independence allows a database to be

structurally changed , it means data can be;• Added and deleted or data attributes altered with

minimum disruption to the existing system• This implies that application programs are not

required to have detailed knowledge of the records layout, it means when a record layout is changed like fields added, deleted, changed in size then fewer application programs or none would be changed


Data Independence….• There are two distinct levels of data

independence;– Logical data independence– Physical data independence

• Logical data independence– Insulates application programs from logical

operations such as combining two records into one or splitting an existing record into two or more records


Data independence….

• Physical data independence– Indicates that the physical storage structures or

devices used for storing data could be changed, this happens without needing a change in the record structure or application programs


Database Administration Roles• Database administration –Centrally

controlling the database– Implemented by a person or group of persons

under the supervision of a knowledgeable person called Administrator, this person known as Database Administrator (DBA)

– DBA is responsible for supervising the creation, modification and maintenance of the database

The DBA controls the database structure and sets up the definition for physical as well as logical implementation of the database.


Database Administration Roles..

• Implementing Security Features,– DBA maintains the integrity of a database

– DBA maintains that the database is not accessible by unauthorised users,

– DBA is responsible for granting permission to use the database and stores the profile of each user

– The user profile can be used by the DBA to verify that a particular user is allowed to access and perform a given operation on database within the limited time frame


Database Administration Roles…

• Measures Against Data Loss– DBA is responsible for defining procedures to

recover data from failures –human natural, or hardware malfunctioning with minimum loss

• DBMS Users– The users of a database can be classified

depending on their degree of expertise or their mode of interactions with the DBMS.



• DBMS Users…..– The user can be classified as..

• Naïve Users• Online Users• Application Programmers• BDAs

• Naïve Users– Are those users who need not be aware of the presence of the

database system or any other system supporting their usage– Example, the users of an Automatic Teller Machine fall in

this category.



• Naïve Users…– The user is instructed through each step of a transaction, user

respond by pressing a coded key or numeric value

– Operations that can be performed by Naïve user are very limited and affect on precise portion of the database

Naïve users are ‘end users of the database who work through a menu driven application program where the type and range of response is always indicated to the user’

( Jain et al., 2002)



• Online Users– Are those users who may communicate with the

database directly via an online terminal or indirectly via a user interface and application program

– These users are aware of the presence of the database system and may have acquired a certain amount of expertise with the limited interaction they are permitted with a database



• Application programmers– Professional programmers, who are responsible

for developing application programs or user interface

• Database Administrator– DBA is a knowledgeable person who is

responsible for the physical design and management of the database


Data Dictionary• A Data Dictionary is a database about databases, it holds the

following information about each data element in the databases;– Name– Type– Range of values– Source– Access authorization– Indicates which application programs use the data.

• A data dictionary may be a stand-alone information system used for management and documentation purposes, or it may be an integral part of the database management system.

• Data dictionary is used to actually control the database operations, data integrity and accuracy


Data Dictionary…..

• Importance of Data Dictionary– It provides the name of a data element, its

description, and data structure in which may be found

– Provides great assistance in producing a report of where a data element is used in all programs that mention it

– It is possible to search for a data name, provided keywords that describe that name


Database Processing

Data Items

Database

Relationships

Constraints

SchemaFigure 1, Components of a Database


Database processing…..

• What is a Database?– A collection of data designed to be used by different people,– Organised in such a way that a computer program can quickly select

desired piece of information– A database consists of four elements;

• Data• Relationships• Constraints• Schema

• Data– Binary computer representations of stored logical entities– They are distinct piece of information usually formatted in a special

way.– The term data is often used to distinguish binary (machine-readable)

information from textual (human-readable) information.


Database Processing….– Example, some applications make a distinction

between data files (files that contain binary data) and text files (files that contain ASCII data)

– In database management systems, data files are the files that store the database information whereas other –index files and data dictionaries, stores administrative information known as metadata



• Relationships– Relationships represent a correspondence between the various

data elements

• Constraints– Are predicates that define correct database states.

• Schema – Describes the organisation of data and relationships within the

database.– Defines various views of the database for the use of the system

components of the database management system and for the application’s security as in figure 2



• Schema…– It separates the physical aspects of data storage from the

logical aspects of the representation– As in figure 2,

• The internal schema defines how and where data are organised in physical data storage

• The conceptual schema defines the stored data structures in terms of the database model used.

• The external schema defines a view/s of the database for particular users. In this case the database management system provides services for accessing the database whilst maintaining the required correctness and consistency of the stored data


Database processing…..External Schema 1

Physical Database

External Schema 2 External Schema N

Global Conceptual Schema

Internal Schema

……….

Figure 2, Organisation of a Database



• Why a Database– Why should an organisation have an integrated database to store

its operational data?– Deficiencies of pre-database information processing include (but

not limit to) the following…• Data inconsistency• Lack data integrity• Data repetition or redundancy• Interdependence between programs and data files• Lack of foolproof data security mechanisms• Lack of coordination across applications using common data• Non-uniform back-up and recovery methods• Encoded data


Database processing…..• The advantage of having the data in a database are;

– Redundancy can be reduced –having a centralised database redundancy or multiple copies of the same data can be reduced

– Inconsistency can be avoided –this depends on data redundancy, which means when the same data is duplicated and changes are made at one site, which is not propagated to the other site, then it gives rise to inconsistency. So if the redundancy is removed chances of having inconsistent data is also removed

– Data can be shared –the existing application can share data in a database

– Standards can be enforced –with the central control of the database, the DBA can enforce standards

– Security restrictions can be applied –the DBA can define authorisation checks to be carried out wherever access to sensitive data is attempted.


Database processing…..– Integrity can be maintained –integrity means

that the data in the database is accurate. Centralised control of the data helps in permitting the administrator to define integrity constraints to the data in the database

– Conflicting requirement can be balanced –database designers can be able to create database that is the best for the organisation by knowing the overall requirements.



• Characteristics of Data in a Database– Shared –a data in a database are shared among different users and

applications– Persistence –data in a database exist permanently in the sense the data can

live beyond the scope of the process that created– Validity/Integrity/ Correctness –data should be correct with respect to the

real world entity that they represent– Security –data should be protected from unauthorised access– Consistency –whenever more that one data element in a database represents

related real-world values, the values should be consistent with respect to the relationship

– Non-Redundancy –no two data items in a database should represent the same real-world entity

– Independence –the three levels in the schema (internal, conceptual and external) should be independent of each other so that changes in the schema at one level should not affect the other levels


Types of Database Language

• There are three types of database languages– DDL ( Data Definition Language)– DML (Data Manipulation Language)– DCL (Data Control Language)


Types of Database Language…

• DDL– Used to define data and their relationships to

other types of data– Used to formulate schema-level concepts– Mainly used to create files, databases, data

dictionaries, and tables within databases.– Defines the format or schema of the database


Data Definition Language…– It allows specification of following information

about each tables• The schema of each table

• The integrity constraints

• The set of values associated with each attribute

• The security and authorization information for each table

• The physical storage structure of each table on disk

The SQL commands that are used to create database objects are known as Data Definition Language or DDL


Types of Database Language……

• DML – DML is a language which deals with the processing or

manipulation of various database objects

– It provides for the program interface to open and close database, find records in files, navigate through the records, add new records and change or delete existing records

– To formulate changes to be effected in a database instance

The SQL commands that are used to manipulate data within database objects are called Data Manipulation Language or DML


Types of Database Language……

• DCL – DCL is a language which used to improve security features

and thus prevents unauthorised access to data in the database

– Security is provided by granting or revoking privileges on a user

– Privileges determines whether or not a user can execute a given command or a command can be executed on specific groups of data

The SQL commands that are used to control the behaviour of database objects are called Data Control Language or DCL


Database Management Systems (DBMS)

• Outline – Introduction to DBMS– Database Architecture – Database Management System– Why DBMS– Types of DBMS

About the Author My name is Aiwinia Temba. I grew up in Kilimanjaro until I was 25 and then I moved down to Moshi, Marangu, where I live now. I began going to college down here but soon dropped out once I realized it wasn’t for me. Sure, I was interested in computers and Web Programming, but most of the courses I was taking in college were totally unrelated. I dropped out figuring that I would be able to learn more on my own than any college could ever teach me. So I began reading computer books and he works as a freelance developer in teaching computers science since 2013 and over the years has written several articles an, programmer and technical writer/editor. He has been involved d tutorials on Office Applications and Web Programming. A lot.

Shortly after reading a few books on web design, I was hooked. I wanted to know everything and anything about it. I was designing websites any chance I could. I spent almost all of my savings buying more books on different programming languages and other nerdy computer gear. I was addicted. The whole concept of computer and programming fascinated me. As I continued to study more and more, I began to realize that most of the books seemed to lack excitement. The material was useful, but they were far from entertaining. I tried to look online for a more interesting source of learning but to no success. That's when I discovered YouTube.