New answers tagged erd
Here are the layers of abstraction that you need to go through to track who has (pays for) a GSM phone: Note that this is good for a point in time. If you need to track changes over time then everything becomes many-to-many with start/end dates in the intersection entities.
The core of the database must be the account, also the customers. They are giving the money for the company, there isn't any other possibility. Logically everything should reference some of an account. Second, the users authentifies themselves for the network of the company by their sim ids. Every sim card should have exactly one account (which will pay for ...
You are using the export graphics feature in Toad but you should instead use the print feature, but instead just printing it, print it to PDF. This will give you non-blurry ER-diagrams.
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