Database 3 Conceptual Modeling And Er

February 23 , 2002 Dr. A. K. Ramani 11

DESIGN METHODS

In previous section– General steps in DB development process , ISA ,EDM

– Database Architectures

AimDesign of conceptual Data Model

Objectives

• Understand – Conceptual Data Modeling

– Concepts of E-R Modeling

– Model Example & Limitations

RECAPRECAP


DESIGN METHODS

Purpose:– create detailed specification of internal documents and tasks from

the EDMInput:

– EDM, usage statistics, and other information gathered during the analysis

Output:– ER-Diagram, Data Representation, Constraints, Task

DecompositionsTechniques:

– data modeling – top-down decomposition of tasks until their specification is

sufficiently detailed to allow a programmer to implement them– task decomposition may result in tasks replacing the original task or

in subtasks controlled by the original taskTools: ER-Model

APPROACHAPPROACH


DESIGN METHODS

To build a

What is 1st Step ?What are the choices,Why ?• User Requirements

- User is not sure - Precise specification is difficult

• Communication Problems- Analyst & user communication- User not willing to take responsibility

Technical - Skills of modeler - Design Methodology – Non

Standard

CONCEPTUAL MODELCONCEPTUAL MODEL


DESIGN METHODS

Feasibility study

Requirement Analysis & Specifications

Data Modeling Process Modeling

Implementation Prototyping Testing

DESIGN APPROACHDESIGN APPROACH


DESIGN METHODS

Requirements Collection & Analysis

Conceptual Design (G)

Logical Design (Blue Print)

Physical Design

Application Design

Methods Req. Collection

Conceptual Model

Data Base System

DBMS

Tools , OS

Requirements Specs

Conceptual Database Model

Logical Models Performance Tests

Final Schema

Application PGMS

DESIGN PHASESDESIGN PHASES


DESIGN METHODS

Conceptual Design

Logical Design

Physical Design

Application Design

Requirement Collection & Analysis

C,Windows,Power Builder

ORACLE

Relational DBs

ER & ERR Model

Questionnaire & Interview

DESIGN METHODSDESIGN METHODS


DESIGN METHODS

• Models can be useful when we want to examine or manage part of the real world

• The costs of using a model are often considerably lower than the costs of using or experimenting with the real world itself

• Examples:– airplane simulator– nuclear power plant simulator– flood warning system– model of US economy– model of a heat reservoir– map

WHY TO USE MODELWHY TO USE MODEL


DESIGN METHODS

A Map Is a Model of Reality

MODEL OF REALITYMODEL OF REALITY


DESIGN METHODS

• A model is a means of communication• Users of a model must have a certain amount of

knowledge in common• A model on emphasized selected aspects• A model is described in some language• A model can be erroneous• A message to map makers: “Highways are not

painted red, rivers don’t have county lines running down the middle, and you can’t see contour lines on a mountain” [Kent 78]

MODEL TO RAISE QUESTIONMODEL TO RAISE QUESTION


DESIGN METHODS

– A process that construct an abstract model which represents the entities,relationships and activities of an enterprise of real world

– Putting a Real World Object on to Paper

Purpose of model is to sharpen the question

MYCOM.COM

US $ 10 b

MCA/MMS

IIPS

CONCEPTUAL MODELINGCONCEPTUAL MODELING


DESIGN METHODS

Why Conceptual Modeling ?• Obtain better understanding of business• Enable the end-user communication• Discover design errors at early stage• Build a Solid Foundation• Ensure the quality• A DBMS independent DB designWhat to Model ?• Static information

– Data - Entities– Associations - Relationship among entities

• Dynamic Information– Process – operations/transactions– Integrity constraints – Business Rules / Regulations

CONCEPTUAL MODELINGCONCEPTUAL MODELING


DESIGN METHODS

• Process - Oriented Approach– Focus on activities, process & operations

Data Flow Diagram

• Data – Oriented Approach– Focus on data & their relationship– Characteristics of Data captured– Data more complex than process– Rich data source is the GOAL– Data is more stable than process– Data Orientation - Longer life

• Object – Oriented ApproachCombine data and process

CONCEPTUAL MODELING APPROACHESCONCEPTUAL MODELING APPROACHES


DESIGN METHODS

• Entity – relationship model (ER) introduced in 1976 by Peter Chen

• Extended ER model (EER) expanded the original ER with new concepts

Lecturer Course

SSN

NameTeach

ER MODELINGER MODELING

Entity• An Entity is a conceptual object

• Physically or conceptually exists

• Usually a noun in requirement specification

E.g. Lecturer , Course , Movie , Sales-order


DESIGN METHODS

• Collection of Entities have same properties• An entity instance is a single occurrence of entity

type• Described once in metadata• A noun in requirement specifications• A true data entity have many instances,each with

distinguishing feature• A strong entity – exists independently like student ,

Course , Car• A weak entity – existence depends upon other entity

(identifying owner)• Dependent

ENTITY TYPESENTITY TYPES


DESIGN METHODS

• Property , description of entities and entity types• Attribute type ( domain)

– Define all possible attribute values

• Attribute value , associated with individual entities• A noun or an objective in requirement specifications

IM-99-02Student

ID

DoB

Singh

4-9-77

Entities – Attributes

•Entities have ‘independent’ meaning e.g. Car , Student

•Attributes have no independent meaning ? ID

ATTRIBUTEATTRIBUTE


DESIGN METHODS

• Uniquely identify individual instances of an entity

type– A key refers to one or a group of attributes as a whole– A key attribute refers to a component of a composite

key– Definition of a key changes with Data Semantics

• An entity type may have few keys – Primary key – One of candidate key– Secondary key – Other keys

• The primary key attribute (s) underlined• Choose key – will not change• Choose key – Not Null• Avoid INTELLIGENT KEYS

KEY ATTRIBUTEKEY ATTRIBUTE


DESIGN METHODS

• Simple attribute– Can’t be broken into smaller values– Contains only atomic values

• Composite attribute– Has component attribute

• Single valued attribute– One only per attribute

• Multi – Valued attribute– Contains multiple values

ATTRIBUTE CLASSIFICATIONATTRIBUTE CLASSIFICATION


DESIGN METHODS

Student

Roll No

Skill

Dob

F.Name

M.Name

L.Name

Name

Degree

EXAMPLEEXAMPLE


DESIGN METHODS

• It is an association among instances of one or more

entities involved.– Label as– Verb in requirement specifications,in present tense &

descriptive– Example

– Model associations, not actions and process

Student Course

Faculty

Teach

take

advise

RELATIONSHIPRELATIONSHIP


DESIGN METHODS

• How is an entity linked to relationship ? [Participation]

• How many relationship instances is an entity permitted to be linked to ? [cardinality]

• Relationship instance is an association between entity instances, where each instance includes exactly one entity from each participating entity type

Student Advise Faculty

Akr

Trupti

Kris

Ram

Mohan

Singh

JUSTIFICATIONJUSTIFICATION


DESIGN METHODS

E1E2R

min,max min,max

Participation

0 – Partial

1 - Total

Cardinality

1 - - One

M - - More than One

O - - One

Advise Faculty

X

Z

Y

A

B

CD

Student

CARDINALITY AND PARTICIPATIONCARDINALITY AND PARTICIPATION


DESIGN METHODS

Unary Relationship

Binary Relationship

Ternary/N-ary Relationship

RELATIONSHIP DEGREESRELATIONSHIP DEGREES


DESIGN METHODS

Person Married

(0,1)

(0,1)

Employee Manager

(0,m)

(0,1)

Unary RelationshipRELATIONSHIP DEGREERELATIONSHIP DEGREE


DESIGN METHODS

One –to-one binary RelationshipA BCD

X

Y

Z

A

One –to-Many binary Relationship

BCD

X

Y Z

E1 E2(1, 1) (0, m)

BINARY RELATIONSHIPBINARY RELATIONSHIP


DESIGN METHODS

Many to Many binary Relationship

E1 E2R1(0, m) (1, m)

X

Y

Z

A

B

C

D

BINARY RELATIONSHIPBINARY RELATIONSHIP

Justification


DESIGN METHODSCustomer

SELL

SalesmanCar

TERNARY RELATIONSHIPTERNARY RELATIONSHIP

CAR REP(0,1) (0, m)

Sell

Customer

(0,M)


DESIGN METHODS

Unary

n-aryto

RELATIONSHIP DEGREERELATIONSHIP DEGREE


DESIGN METHODS

Relationship attributes• Attributes describing relationship, like when ,where, what

FacultyStudent Advise

MemoTime

Date

• A relationship instance must include all participants

• Need to be careful when converted to binary relationship

RELATIONSHIP ATTRIBUTESRELATIONSHIP ATTRIBUTES


DESIGN METHODS

Attributes on a relationship might suggest to convert it to entity , termed (---) as associative entity.

CourseEMP Completes

Date

m m

CERT

Date Number

ASSOCIATIVE ENTITYASSOCIATIVE ENTITY


DESIGN METHODS

• Conditions– Result entity independent meaning

– Result entity participates in one or more other relationships

Other Notations

Mandatory One

Mandatory Many

Optional One

Optional Many

CONDITIONS AND NOTATIONSCONDITIONS AND NOTATIONS


DESIGN METHODS

BASIC E-R NOTATIONBASIC E-R NOTATION


DESIGN METHODS

SAMPLE ER DIAGRAMSAMPLE ER DIAGRAM


DESIGN METHODS

• Conceptual Modeling – important skill• Conceptual Schema important design

document – independent of DBMS• Entities , types• Relationships Unary – n-ary• Associations

– Cardinality (Connectivity)– Participation (Degree)

SUMMARYSUMMARY

Database 3 Conceptual Modeling And Er

Education

abstract model

ermodel approach

entity relationship

standard conceptual

true data entity

data representation

goal data

data semantics