The document discusses entity relationship diagrams and their components. An entity represents a category of data, and an attribute contains a subgroup of information within an entity. Relationship types in ER diagrams include mandatory, optional, many-to-one, one-to-many, and recursive. Many-to-many relationships should be avoided by dividing them into two one-to-many relationships using a joining table. Examples of different relationship types and resolving many-to-many relationships are provided.

1. INFM 603 – Information Technology
and Organizational Context
Lecture 8
Entity Relationship Diagrams

2. 2
Entity
• “An entity is a business object that
represents a group, or category of data.”1
• Do we know a similar concept?
1) Stephens, R.K. and Plew. R.R., 2001. Database Design. SAMS, Indianapolis , IN.

3. 3
Attribute
• “An attribute is a sub-group of information
within an entity.”1
• Do we know a similar concept?
1) Stephens, R.K. and Plew. R.R., 2001. Database Design. SAMS, Indianapolis , IN.

4. 4
Entity Relationship Models
• Mandatory Relationships
• Optional Relationships
• Many-to-Many Relationships
• One-to-Many Relationships
• One-to-One Relationships
• Recursive Relationships

5. 5
Mandatory, Many-to-Many
INSTRUCTOR STUDENT
INSTRUCTOR STUDENT

6. 6
Optional, Many-to-Many
DEPARTMENT STUDENT
DEPARTMENT STUDENT

7. 7
Optional/Mandatory,
Many-to-Many
INSTRUCTOR SKILL
INSTRUCTOR SKILL

8. 8
Optional/Mandatory,
One-to-Many
PRODUCT VENDOR
PRODUCT VENDOR

9. 9
Mandatory, One-to-One
AUTOMOBILE ENGINE
AUTOMOBILE ENGINE

10. 10
Recursive
EMPLOYEE
supervises
is supervised by

11. 11
Resolving Many-to-Many
Relationships
• Many-to-many relationships should be
avoided. We can resolve a many-to-many
relationship by dividing it into two one-to-
many relationships.

12. 12
Resolving Many-to-Many
Relationships
SALES ORDERS INV. ITEMS
SALES ORDERS INV. ITEMSORDER ITEMS

13. 13
Example (ER Diagram)
SALES ORDERS
INV. ITEMSORDER ITEMS
CLERKSCUSTOMERS