DBMS NORMALIZATION 2nd Normalization Form - database-normalization

Question

Voter(voter_id, voter_name, residential_address, current_city, current_state, current_postal_code).
Postal code is unique for each city and state and each address has only one postal code.
In normalization terms, Voter is in 2nf or 3nf?

Answer 1

To check its highest normal form, follow this basic steps:
First rename the attributes of "Voter" for simplicity.
voter_id as "A"
voter_name as "B"
residential_address as "C"
current_city as "D"
current_state as "E"
current_postal_code as "F"
According to given FD's : {DE -> F , C -> F }
3.Here Candidate keys are: {ABCDE}.
hence,
Prime attributes (5): {A,B,C,D,E} ,
Non Prime attributes (1): {F}
For 2NF:
"Partial Dependencies are not allowed".
Means, A part of candidate key should not determine a non prime attributes.
here ,partial dependencies are : {DE -> F , C -> F }
So, this table is not in 2NF.
**To be into 2NF ,relation should be decompose like this:
R1 ={DEF},
R2 = {CF}
R3 = {ABCDE}
Hope this helps. For more detail like how to decompose a table and all, you can also refer : Detailed explanation of Normal forms

Answer 2

Normalization through BCNF is based on functional dependencies. It's not based on column names, although that seems to be what university students are being taught based on their questions on SO.
I'd presume that "voter_id" is a surrogate key, but that's just educated guesswork. (And that's not a good basis for designing databases.) If it's a surrogate key, then "voter_id" is unique, so we have this FD.
voter_id -> voter_name, residential_address, current_city, current_state, current_postal_code
You said, "Postal code is unique for each city and state . . .", so we also have this FD.
current_city, current_state -> current_postal_code
Finally, you said, ". . . each address has only one postal code".
Based on my experience, I think it's unlikely that you meant residential_address -> current_postal_code. I think you meant that residential_address, current_city, current_state -> current_postal_code. But we already know that current_city, current_state -> current_postal_code, so this doesn't tell us anything useful about functional dependencies.
If there are only these two functional dependencies, then the only candidate key for "voters" is "voter_id".
2NF is concerned with partial key dependencies. The only candidate key is a single column. Therefore, partial key dependencies can't exist. So "voters" is in 2NF.
3NF is concerned with transitive dependencies. There's at least one: voter_id -> current_city, current_state, and current_city, current_state -> current_postal_code. So "voters" is not in 3NF.