1. ITS232 Introduction To Database Management Systems
CHAPTER 4
Entity Relationship (E-R) Modeling
(ERD)
Siti Nurbaya Ismail
Faculty of Computer Science & Mathematics,
Universiti Teknologi MARA (UiTM), Kedah
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2. Chapter 4: Entity Relationship (E-R) Modeling
4.0 Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (ER) Model 4.2 Developing An E-R Diagram 4.3 Database Design Challenges

3. Chapter 4: Entity Relationship (E-R) Modeling Basic Modeling Concept
A model is description or analogy used to visualize something that cannot be directly observed.

4. Chapter 4: Entity Relationship (E-R) Modeling Basic Modeling Concept
Relatively simple representations of complex real world data structures
Represents:
data structures and their characteristics
relation and constraints
Can be physical or abstract:
car, student = physical
subject, register = abstract
Used by database designer as:
communications tools to communicate and understanding between a client and the database designer, which the database to be develop.

5. Chapter 4: Entity Relationship (E-R) Modeling Basic Modeling Concept
The importance of data modeling:
Data
constitute the most basic information units employed by a system
Application
is created to manage data and to transform data to information
View
different people views the same data differently based on their understanding
Model
helps different user to have the holistic view of the same data

6. Chapter 4: Entity Relationship (E-R) Modeling Basic Modeling Concept
Three Level ANSI-SPARC Architecture
View 1
View 2
View n
Conceptual Schema
Internal Schema
Database
User n
User 2
User 1 …
-user’s view
External Model
1. External level
Conceptual Model
-designer’s view
-h/w independent
-s/w independent
ERD
2. Conceptual level
-DBMS’s view
-h/w independent
-s/w dependent
Internal Model
3. Internal level
-h/w dependent
-s/w dependent
Physical Model
Physical data
organization

7. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model
Based on the set theory and the relational theory, it is used as tools to:
translate different views of data among managers, users and programmers to fit into a common work
define data processing and constraints to help meet the different views
help implement the database
considered as a stage in a database design preceding the relational database modeling
gives data structures representation of:
what information have to be stored
the relationships between informational elements and constraint on the data structure
relationship

8. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model
ER model forms the basis of an ER diagram (ERD)
ERD represents conceptual database as viewed by end user
ERDs depict database’s main components:
Entities
Attributes
Relationships

9. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model: Entity
Entity
Refers to entity set and not to single entity occurrence
Corresponds to table and not to row in relational environment
In both Chen and Crow’s Foot models, entity is represented by rectangle containing entity’s name
Entity name, a noun, is usually written in capital letters

10. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model: Attribute
Attribute
Characteristics of entities
Property that explains about entity
Correspondents to fields of a table
Primary key are underline with a straight line
Foreign key are underline with dotted line or an *
Chen Model
attributes are represented by ovals and are connected to entity rectangle with a line
each oval contains the name of attribute it represents
Crow’s Foot Model
attributes are written in attribute box below entity rectangle

11. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model
The Attributes of the STUDENT entity: Chen & Crow’s Foot

12. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (E-R) Model: Relationship
Relationship
Associates between entities
Logical interaction among the entities in a relational database
Operate in both directions
Chen Model
Crow’s Foot Model

13. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram
Development of ER model is an Iterative Process that involved:
Step1:
General narrative of organizational operations developed
Step2:
Basic E-R Model graphically depicted and reviewed
Step3:
Modifications made to incorporate newly discovered ER components
Repeat process:
Until designers and users agree on complete E-R Diagram

14. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Model Components
ENTITY
Variations of entity:
Weak
Recursive
Composite
Supertype/Subtype
ATTRIBUTE
Types of attribute:
Simple attributes
Composite attributes
Multivalued attributes
Derived attributes
RELATIONSHIP
Relationship can be describes by:
Degree of the relationship
Connectivity of the relationship
Cardinality of the relationship
Participation

15. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Entity
Corresponds to table and not to row in relational environment
Represented by rectangle containing entity’s name
Entity name, a noun, is usually written in capital letters
Examlpe: Entity STUDENT with attributes

16. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Weak Entity
Recursive Entity
Composite Entity
Entity Supertype and Subtype

17. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Weak Entity
Existence-dependent
Primary key partially or totally derived from parent entity in relationship
Database designer determines whether an entity is weak based on business rules

18. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity

19. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity

20. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Recursive Entity
Entity set that have relationship with the same entity set
Example: EMPLOYEE entity
EMPLOYEE
employeeNO
employeeNAME
manage 1
employeeMANAGER
EMPLOYEE
employeeNO
employeeNAME
married 1
employeeSPOUSE
employeeNO
employeeNAME
employeeSPOUSE
111
Ali
444
222
Ah Chong
333
Bazil
Sheriz
employeeNO
employeeNAME
employeeMANAGER
111
Ali
333
222
Ah Chong
Bazil
444
Sheriz

21. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Composite Entity
Originally a relationship between 2 entities that involved in M:N relationship
Composite entity takes its primary key from both entities that it bridges
Example: enroll
STUDENT
studentID
studentNAME
enroll M
grade
COURSE
courseID
courseNAME N
STUDENT
STUDENT_COURSE / ENROLL
COURSE
studentID
studentNAME
studentID
courseID
grade
ITS232 A+
CSC318 B+
CSC203 B A-
courseID
courseNAME
ITS232
Database
CSC318 IP
CSC203 OS

22. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Parent-Child relationship
Supertypecontains the shared attributes
an entity type that include distinct subclasses that required to be presented in data model
parent
Subtype contains the unique attributes
an entity type that has a distinct role and also a member of supertype
child

23. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Example: Superype (EMPLOYEE)
Subtype (Engineer & Full-Time)

24. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Have two types of relationship:
Disjoint
Overlapping
Unique subtype
Non-overlapping:
subtypes can be one of the types
Overlapping:
Subtypes can be either one or both of the subtypes
Indicate with: G Gs

25. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Example: Disjoint & Overlap
Overlap
Disjoint G Gs

26. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Example: Disjoint

27. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Entity
Variations of Entity:
Entity Supertype & Subtype
Example: Disjoint & Overlap

28. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes
Represented by ovals that are connected to entity with a line
Oval contains of attribute (field) it represents
PK are underlined with straight line
FK are underlined with doted line or *
Example: Entity STUDENT with attributes
name, course, studentID, address,
STUDENT
studentID
name
course
address

29. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Simple Attributes
Composite Attributes
Multivalued Attributes
Derived Attributes

30. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Simple Attributes
An attribute composed of single component with an independent existence
Cannot be subdivided into smaller components
Example: gender, martial statues
STUDENT
studentID
phoneNO
age
gender
name
address
addressTOWN
addressPOSTCODE
addressNO
Simple Attributes

31. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Composite Attributes
An attribute composed of multiple components,
each with an independent existence
Can be further subdivide to yield additional attributes
Example: name  first, middle, last
address street, city, state, zip
Composite Attributes
STUDENT
studentID
phoneNO
age
gender
name
address
addressTOWN
addressPOSTCODE
addressNO

32. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Multivalued Attributes
attribute that holds multiple values for each occurrence of an entity type
Should not be implemented multivalued attributes in relational database
Can simplifies multivalued attributes by:
Create several attributes
Create new entity of the original multivalued attributes components
Example:
phone number handset,office,home
qualification diploma,degree,master

33. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Multivalued Attributes
Can simplifies multivalued attributes by:
Create several attributes
Create new entity of the original multivalued attributes components
STUDENT
age
gender
address
handsetNO
homephoneNO
studentID
gender
STUDENT
studentID
handsetNO
age
address
CONTACT
has
homephoneNO
studentID*

34. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes
Attributes types:
Derived Attributes
An attributes that represents a value that is derived from the value of related attribute or set of attributes, not necessarily in the same entity type.
Need not be physically stored within database
Example: age, cgpa
STUDENT
studentID
phoneNO
age
gender
name
address
Derived Attributes

35. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Attributes

36. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship
Associations between entities
Logical interaction among the entities in a relational database
Operates in both directions
Naming Relationships:
Relationship name is a verb phrase
Avoid vague names
Defining Relationships:
Definition explains what action is being taken and why it is important
Give examples to clarify the action
Optional participation should be explained
Explain reasons for any explicit maximum cardinality
Explain any restrictions on participation in the relationship
Explain extent of the history that is kept in the relationship
Explain whether an entity instance involved in a relationship instance can transfer participation to another relationship instance

37. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Degree of the relationship
Connectivity of the relationship
Cardinality of the relationship
Participation

38. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Degree of the relationship
Indicates number of associated entities within the relationship
There are three types:
Unary Relationship
Association is maintained within single entity
Binary Relationship
Two entities are associated
c. Ternary Relationship
Three entities are associated

39. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship

40. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Connectivity of the relationship
Logical interaction among entities in a relational database
There are three types:
1:1
1:M
M:N
UiTMBRANCH
have
RECTOR 1 1
STUDENT
under
PROGRAM 1 M 1 M
register N
STUDENT
COURSE

41. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
Express the specific number of entity occurrences associated with one occurrence of the related entity
Function of organizational policy  business rules

42. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
Example 1:
One student can register 1 to 9 courses
One course maximum can have 35 student
(1,9)
(0,35)
STUDENT
register
COURSE N M

43. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
Example 2:
One lecturer can teaches maximum 3 courses
One course can be thought by 1 lecturer only
(0,3)
(1,1)
LECTURER
teach
COURSE M 1

44. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
Example 3:

45. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
Relationship Strength  Existence Dependence
Existence dependence
Entity exists in database only when it is associated with another related entity occurrence
Existence independence
Entity can exist apart from one or more related entities
Sometimes such an entity is referred to as a strong or regular entity

46. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Cardinality of the relationship
From Existence Dependence, exist two relationship strength:
Weak Relationship
Entity not existence-independent on other entity
PK of related entity doesn’t contain PK component of parent entity
Non-Identifying Relationship
Strong Relationship
Existence dependence
PK of related entity contains PK component of parent entity
Identifying Relationship

49. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Database Systems, 9h Edition

50. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship

51. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Participation
Determines whether all or some entity occurrences participates in a relationship
There are two types:
Optional (Partial)
One entity occurrence does not require corresponding entity occurrence in particular relationship
Mandatory (Total)
One entity occurrence requires corresponding entity occurrence in particular relationship

52. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:
Participation
Example 1:
One lecturer can teaches maximum 3 courses
One course can be thought by 1 lecturer only
connectivity
(0,3)
(1,1)
LECTURER
teach
COURSE M 1
One class can be thought
by one lecturer only
‘not all lecturer teach class’
optional participation for course
One lecturer can teaches
maximum 3 classes
cardinality
‘all class are teach’
(mandatory participation for lecturer)
participation

53. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Comparison of E-R Model
Alternate style developed to enable easier use of CASE tools. Chen Model The Chen notation favors conceptual modeling Crow’s Foot Model Crow’s Foot notation favors a more implementation-oriented approach UML Model UML notation can be used for both conceptual and implementation modeling

54. Comparison of E-R Modeling Symbols
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Comparison of E-R Model
Comparison of E-R Modeling Symbols
Cardinality & Participation
Chen Model
Crow’s Foot Model
Entity
Weak Entity
Composite Entity
Relationship line
Relationship
Option Symbol
One (1) Symbol
Many (M) Symbol 1 M

55. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Comparison of E-R Model
Chen Model

56. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.2 Developing An E-R Diagram: Comparison of E-R Model
Crow’s Foot Model

57. Chapter 4: Entity Relationship (E-R) Modeling 4
Chapter 4: Entity Relationship (E-R) Modeling 4.3 Database Design Challenges
Conflicting Goals
Database designers often must make design compromises that are trigged by conflicting goals, such as comply with the design standards, processing speed and information requirements.
In order to do so,
it is very important to have the entities, attributes, and relationships clearly identified and well-defined
there is a need in balancing between the customer needs and a design that meets logical requirements and conventions
The more thinking and modeling is done the less money and time are needed later on for rework
Additional concerns are security, performance, shared access and integrity