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Chapter 6: Databases and Data Warehouses

Page 219-228Data ConceptsIntroduction to MS AccessIntroduction to Relational Databases

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Introduction

To retrieve data or information, data must be stored in an organized manner

Meaning data resources must be structured in some logical manner so that– Can be accessed easily– Processed efficiently– Retrieved quickly– Managed effectively

Example: p224

What is the phone number of customer John Smith?

Who is the customer who rented copy number 4780-3?

What is the phone number of the customer who rented ‘The Ring II’?

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Consequences:

We could ONLY answer the above questions because the data was well organized.

Organization starts with good database design.

Database software make it possible to handle such questions or queries.

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Data Storage Hierarchy:

Data in storage is organized as a hierarchy:– Bits– Bytes– Fields– Records– Files– Database

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Hardware deals with:

Bit: 0 or 1 Byte: Letter A is represented as:

0100 0001 Bits and bytes are the building blocks for

representing data: whether in processing, storage, or telecommunications

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Users deals with: (control by SW)

Field: unit of data consisting of one or more characters (bytes). Example:– Your Name– Your Address– Your Student number

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Users perspective (cont.):

Record: is a collection of related fields Name + Address + Student number Student Record:

– A. B. Buthelezi– J Section– Esikhaweni– 2009012345

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Users perspective (cont.):

File: is a collection of related records The file of all students, described by their Names

Addresses and Student numbers Database: is an organized collection of

integrated files:– UZ database will contain files on Student records,

Employee records, Payroll data, Financial Records, etc

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Key Field

A key field: is a field that is chosen to uniquely identify a record so that it can be easily retrieved and processed:

Surname Initials Student#Buthelezi AB 2009012345Buthelezi BA 2009012347

Summary:

Most businesses and organizations rely on information based on data stored in databases

Its critical to access information– Timely– Complete– Accurate– Valid – And relevant

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Ms Access

Ms Access is DBMS (database management system) that allows you to– Create databases– Add, change and delete data– Sort, filter and search data in database

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Ms Access

Main elements in Ms Access– Tables

Fields and records– Queries– Forms– Reports

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Key concepts:

Understand what a db is Difference between data and information How a db is organized Know some uses of large scale db

– Airline booking systems– Government departments– Banks– Hospitals

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Table

It contains data related to a SINGLE subject Each field contains ONE ELEMENT of data Each field data element is associated with an

APPROPRIATE data TYPE Fields have field properties like

– Size– Format– Default value, etc.

Primary key16

Relationships:

Reason is to minimizing duplication of data Is constructed between two tables by the use of

TWO FIELDS that contain the same data– Have the same field names– Create a link between the tables MATCHING

VALUES 1:1 1:M M:N17

1:1

Each record in the first table have only ONE match in the second table

AND Each record in the second table have only ONE

match in the first table

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1:M

Each record in the first table can have more than one matching record in the second table

AND Each record in the second table have only ONE

match in the first table

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M:N

Each record in the first table have MORE than one match in the second table

AND Each record in the second table have MORE

than one match in the first table

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Example using MS Access:

We like to store data of employees and their insurance detail.

Question: Is there an association between the entities ‘employee’ and ‘insurance’?

Question: What info do we need for employee Question: What info do we need for insurance

Designing: Step 1

Association:– An employee has many insurances– An insurance is taken by an employee

This is a ONE to MANY relationship between employee and insurance

1:M

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Designing: Step 2

Determine the characteristics of each entity or ATTRIBUTES

What describe an Employee? What describe an Insurance?

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Designing: Step 3

Assign data types to each characteristics

– Text– Number– Date– Logical– Currency

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Designing: Step 4

Create a data base SCHEMA representing all the information of the previous steps.

See next slide

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Relational Model Diagram:

Designing: Step 5

Represent Step 4 with a MS Visio diagram A model must be presented graphical

because it– Emphasizes understanding– Communication tool

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Employee:

Surname Salary What about a key field? Staff number Employee record:

– Jones– R100 000– 101

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Insurance:

Insurance Company (Can companies have the same name?) How to identify a company?

Who are they insuring? Employee ID The amount Insurance record:

– Company code– Company name– Employee ID– Amount

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Joining Files/Tables:

Why?– What is the address of AB Buthelezi, who was

insured by the company Six Feet Under Relational DB:

– More than one table are used AND each table contains data about one ASPECT

– Tables are connected: the UNIQUE field of one table will appear in the other

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MS Access:

Create a database: human_resource SAVE it in the C-Drive Create Table: employee using the ‘Design View’Emp_surname as TextEmp_salary as CurrencyEmp_number as Number Key Field?????

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Enter Data:

Enter data by ‘Double-Clicking’ on table Employee

Use the tab key to move between fields Data:

– Ndlovu, 100000, 101– Mfeka, 110000, 102– Ngubane, 120000, 103

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Table ‘Insurance’

Create Table: insurance using the ‘Design View’Ins_code as NumberIns_name as TextIns_amount as CurrencyEmp_number as Number

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Forms:

Enter data in table Insurance using a Form! This is very unique to Access and very

POTENT! 1, six_feet_under, 1000000, 101 2, hambakahle, 2500000, 102 3, sos, 1500000,103

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Form:

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Entering Data:

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Summary: (Database Schema)

Database: human_resource Employee(Emp_surname, Text;Emp_salary,

Currency;Emp_number, Number) Insurance (Ins_code, Number; Ins_name,

Text;Ins_amount, Currency;Emp_number, Number)

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Instance of relational database:

EMPLOYEE

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