Overview
This post summarizes the types of relationships in ER diagrams.
Types of Relationships in ER Diagrams
There are three types of relationships in ER diagrams.
| Type of Relationship | Table Relationship | Line Type |
|---|---|---|
| Dependent Relationship | Child table depends on parent table (parent-child relationship exists between tables) | Solid line (Parent → Child) |
| Independent Relationship | Child table does not depend on parent table (no parent-child relationship exists between tables) | Dotted line (Parent → Child) |
| Many-to-Many Relationship | Many-to-many table relationship | Solid line (Parent ↔ Child) |
Dependent Relationship
-
User
- User No (PK)
- Company No (FK)
- Name
- Email Address
-
User Profile
- User No (FK)
- Age
- Gender
The child table, User Profile, cannot exist without a record in the parent table, User, so it can be said that the child table depends on the parent table.
Independent Relationship
-
User
- User No (PK)
- Company No (FK)
- Name
- Email Address
-
User Profile
- User No (FK)
- Age
- Gender
-
Company
- Company No (PK)
- Company Name
As explained earlier, the relationship between User and User Profile is a dependent relationship.
The relationship between User and Company is independent because a customer can exist without a user, and vice versa.
Many-to-Many Relationship
-
User
- User No (PK)
- Company No (FK)
- Permission No (FK)
- Name
- Email Address
-
Permission
- Permission No (PK)
- User No (FK)
This relationship requires a junction (intermediate, pivot) table.
Thoughts
I want to read more books and delve deeper into this topic.
