Continuing with the Vince's Vinyl scenario from Hands-On Database, create an updated ERD after Normalization ? The diagram could pass the first three levels of normalization. There are a couple of issues, though, that could lead to further normalization: Customers and Sellers can be the same people. This could lead to update anomalies as the same person could have their information in two places. The solution is to create a Person entity that contains all names, phone numbers and email addresses. The person key could represent them in either role in Sale, Request, or Purchase. Another subtle issue relates to the entity Album. If Vince were to remove an album, and it was the only copy of that album, he would lose the album information. Also, there is potential redundancy in Album, since each physical vinyl is treated as an individual item in the table. Multiple copies of the same album would result in multiple entries identical except for purchase date and perhaps condition. To solve this would require separating Album from Inventory and having it contain the title, studio, and date.
Continuing with the Vince's Vinyl scenario from Hands-On
The diagram could pass the first three levels of normalization. There are a couple of issues, though, that could lead to further normalization:
Customers and Sellers can be the same people. This could lead to update anomalies as the same person could have their information in two places. The solution is to create a Person entity that contains all names, phone numbers and email addresses. The person key could represent them in either role in Sale, Request, or Purchase.
Another subtle issue relates to the entity Album. If Vince were to remove an album, and it was the only copy of that album, he would lose the album information. Also, there is potential redundancy in Album, since each physical vinyl is treated as an individual item in the table. Multiple copies of the same album would result in multiple entries identical except for purchase date and perhaps condition. To solve this would require separating Album from Inventory and having it contain the title, studio, and date.
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