Page 74 - CITS - Computer Software Application -TT

COMPUTER SOFTWARE APPLICATION - CITS

1 One-to-One Relationship

If a relationship is such that it links a singular instance of an entity, it is referred to as a one-to-one
relationship.
Example :A woman can be married to a single man, and conversely, a man can be married to a single woman.
2 One-to-many relationship

When only one instance of the entity on the left is connected to multiple instances of the entity on the right
within a relationship, it is referred to as a one-to-many relationship.
Example :Scientists have the capability to create numerous inventions, while the act of inventing a particular
invention is attributed to a specific scientist.
3 Many-to-one relationship

When more than one instances of the entity on the left are linked to a single instance of the entity on the right
through a relationship, it is referred to as a many-to-one relationship.

Example :A student is enrolled in a single course, whereas a course can accommodate multiple students.
4 Many-to-many relationship

A many-to-many relationship arises when multiple instances of the entity on the left are connected with multiple
instances of the entity on the right through the relationship.
Example :An employee can be assigned to multiple projects, and likewise, a project can involve multiple
employees.
Advantages of ER Model

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CITS : IT&ITES - Computer software application - Lesson 18 - 36