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Line 13: ==SERM-Example== [[Image:SERM-example.JPG]] * Customer and article are independent entities * Every order is refered to one customer. Orders without customers are illegal (order is an ER Type). 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 refered 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\|third normal form]] [[de:Structured-Entity-Relationship-Modell]]

Structured entity relationship model: Difference between revisions