Structured entity relationship model: Difference between revisions

Revision as of 14:26, 10 October 2006

Revision as of 14:41, 10 October 2006

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[[Image:SERM-example.JPG]]

* [[Customer|Customer]] and article are independent entities

* Every order is refered to one customer. Orders without [[Customer|customers]] are illegal (order is an ER Type). [[Customer|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|customer]], as well. Invoices without [[Customer|customers]] are illegal. [[Customer|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.