The document discusses entity relationship modeling. It defines key components of ER modeling including entities, attributes, relationships and constraints. Entities can be strong or weak. Relationships can be one to one, one to many, or many to many. Cardinality and participation constraints specify the minimum and maximum occurrences in a relationship. An example ER diagram is provided for a university system with entities for departments, courses, modules, students, and lecturers and the relationships between them.

1. Chapter 12
Entity Relationship
Modeling

2. Characteristics of E-R Modeling
– Proposed by Dr. Peter Chen in 1976
– Semantic data model
– Express the logical properties of an enterprise
database
– No physical DBMS
– Unified Modeling Language (UML)

3. Components of E-R Model
– Entity
– Attribute
– Keys
– Relationship
– Constraints

4. Entity
–An entity is an object that exists and which
is distinguishable from other objects. An
entity can be a person, a place, an object,
an event, or a concept about which an
organization wishes to maintain data

5. Entity
– Different Types of Entities
o Strong entity (parent, owner, dominant)
o Weak entity (child, dependent, or subordinate)
o Associative entity
– Diagram Notation
–

6. Entity
– An Associative Entity is an entity type that
connects the instances of one or more entity
types and contains attributes particular to this
association.
– A Strong Entity type exists independent of
other entity types, while a Weak Entity type
depends on another entity type.

7. Attribute
– Domain
– Types of Attribute
o Simple Attribute
o Composite Attribute
o Single-valued Attribute
o Multi-valued Attribute
o Derived Attribute

8. Keys
–Candidate key
–Primary key
–Composite key

9. Relationship
– Relationships are Meaningful Associations between
or among entities.
– Weak relationships, or identifying relationships, are
connections that exist between a weak entity type
and its owner.

10. Relationship
– Degree of a relationship
o The number (unary, binary, or ternary) of entity
sets that participate in a relationship is called the
degree of relationship.
– Types of Relationship
o Unary (recursive relationship)
o Binary
o Ternary
o Quaternary

11. Relationship

12. Relationship

13. Structural Constraints on
Relationship
– The main type of constraint on relationships is called
Multiplicity.
– The number of possible occurrences of an entity
type that may relate to a single occurrence of an
associated entity type through a particular
relationship.
– One-to-one 1..1
– One-to-many 1..*

14. One to One Relationship

15. One to Many Relationship

16. Many to Many Relationship

17. Multiplicity Constraints
– Multiplicity actually consists of two separate
constraints known as cardinality and
participation.
– The Cardinality of relationship represents the
minimum/maximum number of instances of
entity B that must/can be associated with any
instance of entity A.

18. Cardinality Constraint

19. Example

20. Multiplicity Constraints

21. Multiplicity Constraints
– Participation constraints
– Determines whether all or only some entity
occurrences participate in a relationship.
– Total (mandatory, every one involved)
– Partial (optional, only some involved)
–

23. Problems with ER Models
– Improper relationship (Connection Trap)
– Fan trap (ambiguous pathway)
– Chasm trap (missing pathway)

24. Example
A university consists of a number of departments.
Each department offers several courses. A number
of modules make up each course. Students enrol in
a particular course and take modules towards the
completion of that course. Each module is taught by
a lecturer from the appropriate department, and
each lecturer tutors a group of students

25. Example - Entities
A university consists of a number of departments.
Each department offers several courses. A number of
modules make up each course. Students enrol in a
particular course and take modules towards the
completion of that course. Each module is taught by
a lecturer from the appropriate department, and
each lecturer tutors a group of students

26. Example - E/R Diagram
ModuleCourse
Department
Student
Lecturer
Entities: Department, Course, Module, Lecturer, Student

27. Example - E/R Diagram
ModuleCourse
Department
Student
Lecturer
Offers Each department offers
several courses

28. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
A number of modules make up each courses

29. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
Enrols In
Students enrol in a particular course

30. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
Enrols In
Takes
Students … take modules

31. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
Enrols In
Takes
Teaches
Each module is taught by
a lecturer

32. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
Enrols In
Takes
Employs
Teaches
A lecturer from the
appropriate department

33. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
TutorsEnrols In
Takes
Employs
Teaches
each lecturer tutors a group of students

34. Example - E/R Diagram
ModuleCourse
Department
Student
LecturerIncludes
Offers
TutorsEnrols In
Takes
Employs
Teaches