is 380, a. m. thomason1 database fundamentals-is 380 entity relationship diagram chapter 4 : lecture...

IS 380, A. M. Thomason 1

Database Fundamentals-IS 380

Entity Relationship DiagramChapter 4 : Lecture Notes for Asela M. Thomason


• Understand and use the basic constructs of entity modeling:– Entity– Relationship– Attribute

• Additional concepts:– Subtypes/Super-types– Composite, Associative, Recursive, Exclusive, etc.– Optional/Mandatory– Cardinality

Topic Objectives


Entity Relationship Diagram

Data Dictionary Business DataDocumentation

i.e., policy, constraints, etc.

Decision Log Model Set Integration

DataModel

Data Model Components


• Entity modeling is a formal process of describing data in terms of entities, attributes, and relationships.

What is Entity Modeling?


• A business policy is a required course of action shown to guide decisions.

• A business rule is a business condition under which:– Data items are created, related, and maintained.– Business processes are executed.

What is a Business Rule?


• An entity is a business object important to the organization and describes a person, place, thing, or event about which data is stored.

– May refer to a tangible object in the real world, such as CUSTOMER or PRODUCT

– May refer to an intangible business concept, such as ORDER or INVOICE.

What is an Entity?


CUSTOMER

Diagramming Entities


Noun(singular)

Data Entity Name

Adjective(optional)

Naming Entities


• A good entity definition says only what the entity is.

• It excludes how the entity is used.

Entity Definitions


PurchasingVENDORPARTPURCHASE ORDERINVOICEPURCHASING AGENT

BankingBANKHOUSEHOLDCUSTOMERACCOUNT

Project ManagementPROJECTCLIENTEMPLOYEE

Order ProcessingCUSTOMERORDERPRODUCTSALESPERSONINVOICE

Entity Examples


Customer # N

Customer # 5

Customer # 4

Customer # 3

Customer # 2

Customer # 1

Entity Instance

Entity TypeCUSTOMER

Entity Type Instances


Data Modeling

Sybase Concepts

Process Dynamic Modeling

COURSE

INSTANCETYPE

Entity Type Vs. Entity Instance


PROJECTis assigned to

is staffed byEMPLOYEE

Identify Entity Relationships


PROJECTis assigned to

is staffed by

EMPLOYEE VEHICLEdrives

is driven by

TEACHER STUDENTteaches

is taught by

EMPLOYEE

Identify Entity Relationships


GARMENTfashions

is designed by

DESIGNER GARMENTwears

is worn by

DESIGNER

Relationships Should Be Meaningful


INSURANCEPOLICY

owns

is owned by

CUSTOMER

ownsis owned by

INSURANCEPOLICY

Read right to left below the line(INSURANCE POLICY is owned by CUSTOMER)

Read left to right above the line(CUSTOMER owns INSURANCE POLICY)

Clockwise Convention HoldsWhen Rotated 90 Degrees

CUSTOMER

Diagramming Relationships


One-to-oneRelationshipB

C D

E F

One-to-manyRelationship

Many-to-manyRelationship

(1:1)

(1:M), or(M:1) many-to-one

(M:N)

A

Types of Connectivity


maintainsCURRICULUM

is maintained by

• An instructor maintains one curriculum• A curriculum is maintained by one instructor.

INSTRUCTOR

Connectivity – One-to-one


is offered byCLASS

offers

• A course is offered by many classes• A class offers one course.

COURSE

Connectivity – One-to-many


consists ofCOURSE

is part of

• A curriculum consists of many courses• A course is part of many curriculum.

Connectivity – Many-to-many

CURRICULUM


is placed byCUSTOMER

places

Maximum = ManyMinimum = 0

Relationship Participation: Optional/Mandory

Maximum = ManyMinimum = 0

Cardinality ( min. , max.) (0,10)

Maximum = 10Minimum = 0

Maximum and Minimum Instances

ORDER


is taught byINSTRUCTOR

teachesCLASSCOURSE

CURRICULUM

has scheduled

is maintained by

is scheduled for

maintains

consists of is part of

Exercise – Reading Maximums & Minimums


ACTORMOVIE

SCRIPT

casts

learns fromteachesis made into is filmed from

DRAMATEACHER

acts in

Exercise – Reading Cardinality


ACTORMOVIE

SCRIPT

casts

learns fromteachesis made into is filmed from

DRAMATEACHER

acts in

Possible Solution Identifying Maximums and Minimums


Class

Attribute Name

Naming Attributes

Qualifier


What are the attributes of the following:“Data Modeling is a three-day course.”

Identifying Attributes


ACTORMOVIE

SCRIPT DRAMATEACHER

Exercise – Identifying Maximums and Minimums


To determine where an attribute lives, ask:

“What primary key determines the value of this attribute?”

OR

“What entity does this attribute describe?”

Assigning Attributes


PRODUCT:

CUSTOMER:

SIN

CHECKING ACCOUNT:

Choosing Primary Keys

EMPLOYEE:


INSTRUCTORCOURSE

TitleDepartmentDuration

is taught byName

teaches

• A Key is one or more attributes that will uniquely identify an instance of an entity.

Entity Identifiers


Primary Key Guidelines

• Identify all candidate keys

• Select one to be the primary key

• If no good candidate exists, a non-intelligent key can be generated (Customer ID, Order Number).


DEPARTMENT:

FIXED ASSET:

EMPLOYEE # NAME ADDRESS JOB CODE DEPARTMENT #

DEPARTMENT NAME

INVENTORY # DESCRIPTION ORIGINAL COST

DEPARTMENT #

DEPARTMENT #

Primary KeyForeign Key

Foreign Key

Primary Key

Primary Key

EMPLOYEE DEPARTMENT

FIXED ASSET

Foreign Keys Examples

EMPLOYEE:


Course ID (PK)

has scheduled

is maintained by

maintains


is scheduled for

COURSE

Curriculum ID (PK)

CURRICULUM

Class ID (PK)

CLASS

Instructor ID (PK)

INSTRUCTOR

Defining Foreign Keys


COURSEhas scheduled

is scheduled for

Course ID (PK)

CLASS

Class Name (PK)Course ID (FK)

Defining Relationship Instances


Course ID (PK)

has scheduled

is maintained by

maintains


is scheduled for

COURSE

Curriculum ID (PK)

CURRICULUM

Class ID (PK)

CLASS

Instructor ID (PK)

INSTRUCTOR

Resolving Many-to-Many Relationships


PROJECT:

EMPLOYEE # NAME

Primary Key

EMPLOYEE

Why Is It Important to Resolve Many-to-many Relationships?

EMPLOYEE:

E2E3E7

MCELREATHTAMMISAVIANO

PROJ # DESCRIPTION

P1P2P3

ORDER PROCESSINGMORTAGE LOANSPAYROLL

Primary Key

is assigned to

has assignedPROJECT


EMPLOYEE

How are Many-to-many Relationships Resolved?

is assigned to

has assignedPROJECT

EMPLOYEE ASSIGNMENT PROJECT

Associative Entity (Composite Entity)

Primary key:Employee#Project#

Primary key:

Employee#Primary key:

Project#


ASSIGNMENT:

PROJECT:

EMPLOYEE # NAME

Primary Key

Primary Key

EMPLOYEE

ASSIGNMENT

PROJECT

Relational Table View

EMPLOYEE:

E2E3E7

MCELREATHTAMMISAVIANO

EMP # PROJ #

E2E2E3E4E7

P1P2P1P3P2

START DATE

02/8901/9006/8911/8907/89

HOURS

10050

5007510

PROJ # DESCRIPTION

P1P2P3

ORDER PROCESSINGMORTAGE LOANSPAYROLL

Primary Key


COMMERCIALLOAN

What is a Subtype?

Subtype(Child)

Supertype(Parent)

LOAN

RESIDENTIALLOAN

COMMERCIALCUSTOMER

CUSTOMER

RESIDENTIALCUSTOMER


BANKACCOUNT

Entity Subtyping Rules

OR

CHECKINGACCOUNT

CHECKINGACCOUNT

BANK ACCOUNT

SAVINGSACCOUNT

• Entity subtypes are subdivisions of an entity that represent the same object as the original entity.

SAVINGSACCOUNT

is a is a


Exercise - Subtyping

• Subtypes and draw each of the following entities once by life cycle state and once by variety:

– EMPLOYEE

– INSURANCE POLICY

– FAMILY MEMBER


Possible Solution - Subtyping

VARIETY

LIFE CYCLESTATE

TERM LIFE

INSURANCEPOLICY

VARIABLELIFE

MANAGEMENTEMPLOYEE

EMPLOYEE

UNIONEMPLOYEE

PARENT

FAMILYMEMBER

CHILD

ACTIVEPOLICY

INSURANCEPOLICY

LAPSEDPOLICY

ACTIVEEMPLOYEE

EMPLOYEE

RETIREDEMPLOYEE

ADULT

FAMILYMEMBER

MINOR


GRADUATE

Subtyping Strategies

An entity can be subtyped by:

Variety

STUDENT

UNDER-GRADUATE

MYSTERY

BOOK

ADVENTURE

ADVENTURE

Life Cycle State


When is Subtyping Useful?

• When the business views subsets of an entity differently; for instance, when business policies are different for different subsets.

• When only certain subsets of an entity have a relationship with another entity.

• When the cardinality between two entities is different for one or more subsets.

• When the attributes of an entity vary significantly from subset to subset.


DOCK

Entity Subtypes Example

is moored atGARAGE

OWNER

VEHICLE

is accom-modating is parked in

owns

contains

is owned by

DOCKis moored

at

GARAGE

OWNER

VEHICLEis accom-modating

is parked

in

owns

contains

is owned by

BOAT AUTO

BECOMES

Parent(Supertype) Child

(Subtype)


Resolving Entity Subtypes

Subtypes must be resolved before creating your Physical ERD, model. There are 3 different options:

Option 1: Create dependent entities and preserve the parent entity. ( a dependent entity contains the primary key of another entity, or has an existence dependency on that entity)

BOAT AUTO VEHICLE



Option 2: Create an entity for every subtype and eliminate the parent. The vehicle information will be duplicated in auto and boat.

BOAT AUTO



Option 3: Create an entity that will store all the information for both the supertype and subtype.

VEHICLE


Data Model Types

Conceptual(First draft)

Logical

Physical (Access/Oracle)

Note: These three models do not match the Database book in class. Similar but not exact.


Why is Conceptual Entity Modeling Important?

• It identifies the high-level data requirements of each major business function.

• It portrays the business view of the data.• It illustrates important entity relationships.• It forces you to question and crystallize business

policy.


Characteristics of a Conceptual Entity Model

• Shows Only Important Entities• Based on Partial Understanding• Includes Subtypes• Allows Many-to-many Relationships• Shows Primary Keys• Shows Few or No Non-key Attributes• Is Independent of Physical Constraints


Developing the Conceptual Entity Model

• Identify the major entities• Define the relationships between the major entities• Define entity keys


Conceptual Vs. Logical – What’s the Difference?

All Attributes NormalizedFew Attributes Non-keyAttributes

All Keys and RI RulesPrimary, Some ForeignKeys

Detailed with M:N ResolvedHigh-level, M:NRelationships

All Entities, with Subtypes Resolved

Major Entities and SubtypesEntities

Development ReleaseBusiness AreaScope

LogicalEntity Model

ConceptualEntity Model


Characteristics of a Logical Entity Model

• Shows All Entities• Resolves Subtypes• Resolves All Many-to-many (M:N) Relationships• Identifies and Defines All Attributes• May Identify All Foreign Keys• Is in Third Normal Form• Identifies Domains• Is Independent of Physical Constraints


What Information is Available?

• Detailed Entities and Relationships• Attributes• Statistics and Characteristics

Conceptual Entity Model

Logical Entity Model

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