A co-worker reviews a database design you’ve been working on. In it, they notice

Question

A co-worker reviews a database design you’ve been working on. In it, they notice that you include the following in your customer entity:

Customer Name (Frist, Middle Initial Last)

Customer Address:

i.Street address

ii.City

iii.State

iv. Zip Code

Your co-worker argues that having the City is unnecessary duplication of data, as if you know the zip code, the city can be determined. They also argue that your design violates 3NF (because of the inclusion of both City and Zip).    In addition to your desire to tell him to …, you also want to answer the specific questions. Namely, does this design violate 3NF, and if so why?   If it does violate 3NF, what would it look like (in terms of Entities, Attributions, and Relationships) of the model that doesn’t violate 3NF.   Finally, if it does violate 3NF, what would your rationale be to keep it as is?

Explanation / Answer

I there are 2 tables as follows:

1st one being Customer Name (Frist, Middle Initial Last)

2nd one being

Customer Address:

i.Street address

ii.City

iii.State

iv. Zip Code

then it is 3 nf as there is no transitive dependency . In the 2nd table zip is the primary key.

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