Structured entity relationship model

Aims

1. structuring of large schemes
2. visualization of existence dependency
3. avoidance of inconsistencies
4. avoidance of unnecessary relationshiptypes

   SERM symbols

SERM example

• Customer and article are independent entities
• Every order is referred to one customer. Orders without customers are illegal. Customers without any orders are legal because they are independent Entities.
• To every order there is belonging at least one order item.
• Every order item is related to exactly one order.
• Every invoice is referred to one customer, as well. Invoices without customers are illegal. Customers without any invoice are legal.
• To every invoice there is belonging at least one invoice line item.
• Every invoice line item is related to exactly order item. An order item could be calculated or not.
• SERM is already in the third normal form