Entity Relationship Diagrams. Database Development Process Business Information Requirements...
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Transcript of Entity Relationship Diagrams. Database Development Process Business Information Requirements...
Database Development Process
Database Development Process
Business Information Requirements
Operational Database
Conceptual Data Modeling
Logical Database Design
Physical Database Build
Business view
Systems view
Terminology Terminology LOGICALCONCEPTUAL
DESIGN
ENTITY
RELATIONSHIP
ATTRIBUTE
TABLE
FOREIGN KEY
COLUMN
(Business view) (Systems view)
ANALYSIS
UNIQUE IDENTIFIER
PRIMARY KEY
UNIQUE KEY
Information ModelsInformation Models
• Organize thought processes• Accurately model business data• Communicate with stakeholders• Analyze the scope• Provide sound basis for system
design
• Organize thought processes• Accurately model business data• Communicate with stakeholders• Analyze the scope• Provide sound basis for system
design
CS 450 ERD Conventions
EMPLOYEE DEPARTMENTWorks ForM 1
empnum
entity relationship
attribute
Participation Requirements (optionality)
Cardinality (degree)
key
heldby
the holderof
part of
composedof
RecursiveRelationship
Main Elements of an Oracle ERD
Main Elements of an Oracle ERD
Exclusive Arc
MEMBERSHIP
CUSTOMER# * customer number * first name * last name o other initials
COMPANY
SUPPLIER
OTHERCOMPANY
heldby
the holderof
UniqueIdentifier
Attributes
Relationship
Entity
Super-type
Sub-type
Hardware and Software IndependenceHardware and Software Independence
Agreement Term
Product
Agreement
Code Date Customer Code Description
Agreement Quantity ProductNumber
HIERARCHICAL DATABASE
NETWORK DATABASE
RELATIONAL DATABASE
Agreement Product x
Product yItem 1
Item 2
ENTITY RELATIONSHIP MODEL
Agreement
Item 1
Product X
Item 2
Product X
Relationship DefinitionsRelationship Definitions
• The way one entity relates to another• The business rules that link together
business information needs • What one thing has to do with
another • A named association between entities
• The way one entity relates to another• The business rules that link together
business information needs • What one thing has to do with
another • A named association between entities
Relationship Diagramming Conventions
Relationship Diagramming Conventions
• A line between two entities• Lower case relationship name• Optionality (Minimum cardinality)
• A line between two entities• Lower case relationship name• Optionality (Minimum cardinality)
Optional - may be
Mandatory - must be
One or more
One and only one
• Degree (Maximum cardinality)
• Degree (Maximum cardinality)
Relationship Diagramming Conventions
Relationship Diagramming Conventions
COPY TITLE
many(crow’s foot)
mandatory
optional
one
Relationship SyntaxRelationship Syntax
Each
Subject entity
must beormay be
relationshipname
one or moreorone and only one
entity 1 entity 2
Degree
Object entityOptionality
Name
Entity 1 Entity 2
EMPLOYEE DEPARTMENTassigned to
Each EMPLOYEE must be assigned to one and only one DEPARTMENT
How do you read this?How do you read this?
EMPLOYEE DEPARTMENT
Each DEPARTMENT may be responsible for one or more EMPLOYEES
responsible for
How do you read this?How do you read this?
EMPLOYEE DEPARTMENTassigned to
Each EMPLOYEE must be assigned to one and only one DEPARTMENT
EMPLOYEE DEPARTMENT
Each DEPARTMENT may be responsible for one or more EMPLOYEES
responsible for
Full Reading of RelationshipFull Reading of Relationship
Each STUDENT may be enrolled in one or more COURSES
Each COURSE may be taken by one or more STUDENTS
taken by
enrolled in
STUDENT COURSE
How do you read this?How do you read this?
Analyzing and Modeling Relationships
Analyzing and Modeling Relationships
1 Determine the existence of a relationship2 Name each direction of the relationship3 Determine the degree of each direction of
the relationship4 Determine the optionality of each direction
of the relationship5 Read the relationship aloud to validate it
1 Determine the existence of a relationship2 Name each direction of the relationship3 Determine the degree of each direction of
the relationship4 Determine the optionality of each direction
of the relationship5 Read the relationship aloud to validate it
Oracle’s Layout GuidelinesOracle’s Layout Guidelines
Dead Crows Fly East !
Child Entity
Parent Entity (1)
Parent Entity (2)
AttributesAttributesBadge Number - Identifies an employee
Name - Qualifies an employee
Payroll category (weekly or salaried) - Classifies an employee
Date of birth - Quantifies an employee
Employment status (active, leave, terminated) - Classifies of an employee
Finding AttributesFinding Attributes
Is this attribute really needed ?
Beware of obsolete requirements from previous systems
Beware of derived data
Attribute Diagramming Conventions
Attribute Diagramming Conventions
EMPLOYEE
badge numfirst namelast name
payroll num
date of birthemployment status
• Inside the entity's soft box
• Singular
• Lowercase
• Inside the entity's soft box
• Singular
• Lowercase
Meaningful ComponentsMeaningful Components
PERSON
name
PERSON
last namefirst name
ITEM
code
ITEM
typevendornum
Break down aggregate attributes
Verify for Single ValueVerify for Single ValueRENTAL
transaction date
total amount paid
item
Yes, more than one item may be rented at a time. An entity is missing.
Can an attribute have more than one value for one instance of the entity?
RENTAL
transaction date
total amount paid
RENTAL ITEM
item num
Attributes Which have Attributes
Attributes Which have Attributes
Does information need to be stored about any of the attributes?
Yes, review details. An entity is missing.
TITLE
product codetitledescriptionreview details
REVIEW
authorcommentdate recorded
product codetitledescriptionreview details
TITLE
Finding Common or Derived Data
Finding Common or Derived Data
• Count • Total• Maximum, Minimum, Average• Calculation
• Count • Total• Maximum, Minimum, Average• Calculation
Derived attributes are redundant and can lead to inconsistent values
12 08 30 22----72----
Attribute OptionalityAttribute Optionality
• A value must be stored for each entity instance• Tagged with
• A value must be stored for each entity instance• Tagged with
Mandatory Attributes
Optional Attributes
• A value may be stored for each entity instance
• Tagged with o
• A value may be stored for each entity instance
• Tagged with o
*
Attribute OptionalityAttribute Optionality
EMPLOYEE
badge num
first name
last name
title
***o weight
o
Attribute Details and Volumes
Attribute Details and Volumes
Attribute - * Engine Size
Format Type NumberMaximum length 4Average length 4Decimal place 1Unit of measure ccAllowable values 900,1000,1500,1800,2000
Volume Initial 100%
Diagrammer Behavior
• Definition changes are stored in Definition changes are stored in Repository even if the diagram Repository even if the diagram is not saved.is not saved.
• Saving a diagram saves the Saving a diagram saves the layout.layout.
• Diagrams are not synchronized Diagrams are not synchronized automatically.automatically.
• Requerying is your Requerying is your responsibility.responsibility.
• Diagrams can be exported to, Diagrams can be exported to, for example, Word documents.for example, Word documents.