Database Chapter02-01

8/10/2019 Database Chapter02-01

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CHAPTER 2

DATABASE DESIGN

Database Application

SAK 3408

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Learning Objectives (W2)

Describe the database design phases.

Explain on how to construct E-R diagram.

Transform ERD into Relation.

Use normalization to decompose a relationwith anomalies into well-structured relations.

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The goal of any information system is toadd value for the user.

Reduce costs

Increase sales/revenue

Provide competitive advantage The need for database design:

Flexible enough to handle future needs

Future developers to understand the

system To communicate with users and IT staff

The important step of all methodologies isto build models of the system.

Introduction

Design

SQL

Program

Best:

Spend your time

on design and SQL.

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Database System Design

User views

of data.

Conceptual

data model.

Customer(CustomerID, Name, Address, )

SalesPerson(EmployeeID, Name, Commission, )

Order(OrderID, OrderDate, CustomerID, EmployeeID, )

OrderItem(OrderID, ItemID, Quantity, Price, )

Item(ItemID, Description, ListPrice, )

Implementation

(relational)

data model.

Physical

data

storage.

Class diagram

that shows

businessentities,

relationships,

and rules.

List of nicely-

behaved tables.

Use data

normalization to

derive the list.

Indexes and

storage methods

to improve

performance.

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Initiation Scope Feasibility Cost & Time estimates

Requirements Analysis User Views & Needs

Forms Reports

Processes & Events Objects & Attributes

Conceptual Design Models

Data flow diagram Entity Relationships Objects

User feedback

Physical Design Table definitions Application development

Queries Forms Reports Application integration

Data storage Security Procedures

Implementation

Training Purchases Data conversion Installation

Evaluation & Review

Design Stages5


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Initial Steps of Design

1. Identify the exact goals of the system.

2. Talk with the users to identify the basic forms

and reports.

3. Identify the data items to be stored.

4. Design the classes (tables) and relationships.

5. Identify any business constraints.

6. Verify the design matches the business rules.

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E-R modela logical representation of the

data for an organization or for a business

area

E-R diagrama graphical representation of

an entity-relationship model

The E-R Model7


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Variations on ER Attribute

Display8

PATIENT

PAT_idnumber

PAT_firstname

PAT_lastname

PAT_addressPAT_city

PAT_state

PAT_birthdate

PAT_zipcode

PAT_homephone

Attributes in Ellipse


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PATIENTPAT_idnumber

PAT_firstname

PAT_lastname

PAT_address

PAT_city

PAT_state

PAT_zipcode

PAT_homephone

PAT_birthdate

Variations on ER Attribute

DisplayPATIENT

PAT_idnumber

PAT_firstname

PAT_lastname

PAT_addressPAT_city

PAT_state

PAT_birthdate

PAT_zipcode

PAT_homephone

Attributes in Rectangle


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Variations on Level of Entity Attribute

Displays10

PatientPAT_idnumber

PAT_firstname

PAT_lastnamePAT_address

PAT_city

PAT_state

PAT_zipcode

PAT_homephone

PAT_birthdate

PatientPAT_idnumber PATIENT

Entity with All Attributes

Entity with Identifier

Attribute OnlyEntity with No Attributes


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Entity

person, place, object, event or concept in the user

environment about which data is to be maintained.

Attribute property or characteristic of an entity type

Relationship

association between the instances of one or moreentity types i.e. link between entities

E-R Model Constructs11


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Entity Identity Example

Person STAF, STUDENT, LECTURER

Place DISTRICT, TOWN, STATE

ObjectEvent

Concept

BUILDING, TOOL, PRODUCT

COURSE, ACCOUNT

REGISTRATION, APPLICATION

Example of Entity types according to its identity

Entity Type

Entity type represents a set or collection of objects

in the real world that share the same properties.

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ER VARIATIONS - CHEN

MODEL

PROFESOR CLASSteaches

profID profName

classID

className

EntityName Verb Phrase AttributeName

Example:


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ER VARIATIONS - CROWS FOOT

MODEL14

name>

Entity

Attribute

Relationship

Verb phr ase

teaches

PROFESSOR

profName

CLASS

classID

Example:

profID

className


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Sample of E-R Diagram

entity relationship

identifier

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attribute


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Sample of E-R Diagram16


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Entitysymbols

Relationship

symbols

Attribute

symbols

A special entitythat is also a

relationship

Basic E-R Notation17


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Entity Type vs. Entity Instance

Entity Type- collection of entities (often

corresponds to a table)

Entity instance- a single occurrence of an entitytype(often corresponds to a row in a table)

Strong vs. Weak Entity Types

Strong Entity Typeentity that exists

independently of other entity types Weak Entity Typeentity type whose existence

depends on some other entity type

Entity18


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75115 Farazila Yusof

75794 Wan Haniza Wan Hassim

76740 Norwani Mohd Zain

77388 Zarawahida Zakaria

77512 Rozita Bt Bahamad

77558 Armamorhana Ahmad

77655 Siti Amrah Zakaria

78436 Siti Nor Haiza Mad Janapi

78447 Noriati Jaminah84781 Emilza Fuad

84817 Azli Kamarudzaman

84858 Faddly Mazlan

84904 Balkhis Diba Mansor

85013 Aina Najmi Shari

85042 Ku Irdawaty Ku Yaakob

Rows represented

entity instances of

the entity type

Entity type: STUDENT

Example of Entity Type vs. Entity

Instance19


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Naming and Defining Entity

Use singular noun.

Should be descriptive and specific. For example: PURCHASE_ORDER and

CUSTOMER_ORDER cannot be named as ORDER

Should be concise. For example:

REGISTRATION_FOR_STUDENT_IN_CLASS

Should be named for the result of the event, notthe activity or process of the event. Forexample: an event of a project managerassigning an employee to work on a project

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Simple vs. Composite Attribute

Simple attributecannot broken into smaller

components

Composite attributecan broken into component parts

Single-Valued vs. Multivalued Attribute

Single-Valuedeach of the attributes has one value

Multivaluedattribute more than one value

Stored vs. Derived Attributes

Stored attributedata input or set

Derived Attributeattribute whose values can be

calculated from related attribute values.

Identifier Attributes

Attribute21


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An attribute

broken into

component parts

An Example of Composite

Attribute22


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Entity with a multivalued attribute (Skill) and derivedattribute (Years_Employed)

Derivedfrom date employed and current date

Multivalued:an employee can have

more than one skill

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Identifier (Primary Key)- An attribute (or

combination of attributes) that uniquely

identifies individual instances of an entity

type

Composite Identifieran identifier that

consists of a composite attribute.

Candidate Keyan attribute that could be akeysatisfies the requirements for being a

key

Identifier (Key)24


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Will not change in value

Will not be null

No intelligent identifiers whose structure

indicates classification, location etc. (e.g.containing locations or people that might

change)

Substitute new, simple keys for long,composite keys

Characteristic of Identifier25


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Simple Key Attribute

The key is underlined

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Composite Key Attribute

The key is composed

of two subparts

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Relationship

Author Book

Relationship name:writes

An author writes one or more books

A book can be written by one or more authors.

Associations between instances of one or

more entity types that is of interest

Given a name that describes its function.

relationship name is an active or a passive verb.


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Relationship Types vs. Relationship Instances The relationship type is modeled as the diamond and

lines between entity types whereas the relationshipinstance is between specific entity instances

Relationships can have attributes These describe features pertaining to the association

between the entities in the relationship

Two entities can have more than one type ofrelationship between them (multiplerelationships)

Associative Entity = combination of relationship

and entity

Relationship29


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Relationship type

Entity and Relationship instances

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Degree of a Relationship is the number of

entity types that participate in it

Unary Relationship

Binary Relationship Ternary Relationship

Degree of Relationship31


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Degree of Relationship ..cont.

One entityrelated to

another of

the same

entity type

Entities of

two differenttypes related

to each otherEntities of three

different types

related to each

other

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OnetoOne

Each entity in the relationship will have exactly one

related entity

OnetoManyAn entity on one side of the relationship can have

many related entities, but an entity on the other

side will have a maximum of one related entity

ManytoMany

Entities on both sides of the relationship can have

many related entities on the other side

Cardinality of Relationship33


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Degree of relationships and Cardinality

(a) Unary relationships

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(b) Binary relationships35


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A simultaneous relationship between instances of threeentity types.

The above E-R diagram shows that: A student can register many courses and a course can be

registered by many students.

A student can have many lectures and a lecture can havemany students.

A lecturer can teach many course and a course can be taughtby many lecturers.

STUDENT COURSE

LECTURER

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(c) Ternary relationships (1)

registers


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Transforming a ternary relationships into a binary relationships

STUDENT COURSE

LECTURER

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Binary relationships

registers

has teaches


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(c) Ternary relationships (2)

Note: a relationship can have attributes of its own

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Cardinality Constraints - the number of instances

of one entity that can or must be associated with

each instance of another entity.

Minimum Cardinality If zero, then optional

If one or more, then mandatory

Maximum Cardinality The maximum number

Cardinality Constraints39


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Cardinality Mandatory and Optional40


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(a) Basic relationship with only maximum cardinalities showing

(b) Mandatory minimum cardinalities

Cardinality Constraints41


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Examples of multiple relationships

Employees and departmentsentities can be related to one

another in more than one way

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Strong vs. Weak Entities, and

Identifying Relationships

Strong entities

exist independently of other types of entities

has its own unique identifier

represented with single-line rectangle

Weak entity dependent on a strong entitycannot exist on its own

Does not have a unique identifier

represented with double-line rectangle Identifying relationship links strong entities to weak entities

represented with double line diamond

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Strong and Weak Entity

Strong entity Weak entityIdentifying relationship

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Its anentityit has attributes

AND its arelationshipit links entities together When should a relationship with attributesinstead be an

associative entity?

All relationships for the associative entity should be many

The associative entity could have meaning independent of

the other entities

The associative entity preferably has a unique identifier, andshould also have other attributes

The associative may be participating in other relationships

other than the entities of the associated relationship

Ternary relationships should be converted to associative

entities

Associative Entity45


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An Example of Associative Entity


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An Example of Associative Entity -

CERTIFICATE

Associative entity involves a rectangle with a diamond inside.

Note that the many-to-many cardinality symbols face toward

the associative entity and not toward the other entities

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(b)Ternary relationship as an associative entity

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For each pair of sentences, identify entitiesand the relationship representing thesentences. "Each student must take one or more modules"

"Each module must be taken by one or morestudent(s)"

"Each customer must receive at least onedelivery"

"Each delivery must be only for one customer" "A client my have an account manager"

Each account manager has only one client"

ERD Exercise (1)49


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An automobile insurance company needs tokeep track of information about vehiclepolicyholders. The company has to storeinformation of customer, car and accident.

Customer information is License_no, nameand address. Customers can own one or morecars, where the car information is Plate_no,model and year. A car not involved or involvedin many accidents. If the car is involved in an

accident the information that will be stored isReport_number, location and date. Each carthat is involved in accident the damageamount will be estimate.

Draw the ERD.

ERD Exercise (2)50


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ERD Exercise (3)

A small company that rents canoes needs a database to track basic informationabout the rental and the canoes. Eventually, the firm wants to identify customers who

cause problems by damaging the canoes, but for now, the managers just want to

track the costs. The managers have outlined the data as a form. Draw an ER

diagram for this case.

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