> For example not everyone has a middle name, but you don't want to go all 5th Normal Form on it.

(actual question) how does 5NF apply here?

I thought that this case could be handled null-free by introducing a separate table

people_middlenames (human_id PK, middlename NOT NULL);

Is it already 5NF? I thought 5NF requires more complex structure of data, like explained in Wikipedia, for example.

Thanks,