Firstly, i suggest you the steps to quickly find a correct normalization of the table, using the example that you brought, showing you the correct normalization.
Define the key
The key is usually defined by its usefulness, or its role in operations like joins (if we need a join lot of times we could choose a key instead of another).
I choose A U B as a key. I usually underline the key, but, because in this board we can't underline text, I will write the key as AB
Define the functional dependencies
You already found the FD, so we can go to the next step.
2NF Normalization
Looking at the FD the correct normalization is:
R1 (the previous big table) (**A**:R3,**B**:R2, C)
AB -> C
(:R2 indicates a foreign key)
In this table we can find the AB -> C functional dependency.
R2 (**B**,F, G, H)
B -> F,
F -> GH
R3 (**A**, D, E, I, J)
A -> DE,
D -> IJ
3NF Normalization
R1 (**A**:R3, **B**:R2, C)
AB -> C
R2 (**B**, F:R4)
B -> F
R3 (**A**, D:R5, E)
A -> DE
R4 (**F**, G, H)
F -> GH
R5 (**D**, I, J)
D -> IJ
Best Answer