1. Entity-Relationship Diagrams
Conceptual Modeling
Entity-Relationship Diagrams

2. E-R Model Constructs
Entities
Relationships
Attributes

3. E-R Model Notation Entity Attribute One-to-many relationship
Many-to-many relationship

4. Example of Relationship Type
COMPLETES
EMPLOYEE
COURSE
A particular employee may complete many courses
A particular course may be completed by many employees

5. Cardinality Constraints
A cardinality constraint specifies the number of instances that can, or must, participate in a relationship.

6. Degree of a Relationship
Refers to the number of entity types that participate in the relationship.
Unary (degree 1)
Binary (degree 2)
Ternary (degree 3)

7. Binary Relationships
Relationship between the instances of two entity types.

8. Example of Binary One-to-One Relationship
ASSIGNMENT
EMPLOYEE
PARKING PLACE
A particular employee is assigned one parking place
A particular parking place may be assigned to only one employee

9. Example of Binary One-to-Many Relationship
MEMBERSHIP
DEPARTMENT
EMPLOYEE
A particular department consists of many employees
A particular employee belongs to one department

10. Example of Binary Many-to-Many Relationship
MEMBERSHIP
EMPLOYEE
COMMITTEE
A particular employee may belong to many committees
A particular committee consists of many employees

11. Unary Relationship
A unary relationship, also called a recursive relationship, is a relationship between the instances of a single entity type.

12. Example of Unary One-to-One Relationship
MARRIAGE
PERSON
A particular person may be married to only one other person

13. Example of Unary One-to_Many Relationship
SUPERVISORY
EMPLOYEE
A particular employee may supervise many employees
A particular employee has only one supervisor

14. Example of Unary Many-to_Many Relationship
BILL_OF_MATERIAL
PART
A particular part may consist of many component parts
A particular part may be the component for many parts

15. Ternary Relationship
A ternary relationship is a simultaneous relationship among the instances of three entity types.

16. Example of Ternary Many-Many-Many Relationship
SKILL
EMPLOYEE
PROJECT
SKILL
ASSIGNMENT
A particular employee may use a particular skill on many projects
In a particular project, a particular skill may be used by many employees
A particular employee working on a particular project may use many skills

17. Another Example of Ternary Many-Many-Many Relationship
PART
VENDOR
WAREHOUSE
SUPPLIES
A particular part , supplied by a particular vendor, may be stored in many warehouses
A particular part, stored in a particular warehouse, may be supplied by many vendors
In a particular warehouse, a particular vendor may supply many parts

18. Example of Ternary Many-Many-One Relationship
SEMESTER
INSTRUCTOR
COURSE
TEACHES
In a particular semester, a particular instructor may teach many courses
A particular instructor may teach a particular course in many semesters
In a particular semester, a particular course is taught by only one instructor

19. Comparing Notation BELONGS_TO EMPLOYEE DEPARTMENT Belongs EMPLOYEE To
Consists_of

20. Example of Composite Attribute