When do you use an ER diagram?

An Entity-Relationship Diagram (ER diagram) is used during the database or system design phase to visually represent the data structure and relationships between entities.

Applications of ER diagrams:

• During system requirements analysis to understand which objects (entities) are involved and how they are related.
• For designing a relational database to determine tables, their attributes, and relationships.
• When documenting an existing system for a better understanding of the data architecture.
• For communication between analysts, developers, and clients to agree on the data structure.

For example, if a order management system is being developed, an ER diagram can show entities like "Customer", "Order", "Product" and the relationships between them (a customer places an order, an order contains products). This simplifies understanding and further implementation.