Entity-relationship diagram (A3.2 Database design)

Entity-relationship diagram (ERD)

Visual representation of entities in db and relationships

Functions

• Acts as documentation for database designs

• Facilitations communication between stakeholders

• Support future development and maintenance of db

• Ensure data integrity and consistency through constraints and well-defined relationships

I. Crow’s foot notation

Type of ERD including modality, cardinality

Modality (I)

Defines optionality of relationship (optional: 0; mandatory: 1)

• Innermost symbol from entity

• Minimum

Cardinality (I)

Max no. of times instance in one entity can be associated with instances in related entity

• Describes type of relationship (one-to-one, etc)

• Maximum 

• Outermost symbol

EXAMPLES

Ex of how to read modality, cardinality