Which normal form does this table violate?

Question

Consider this table:

   +-------+-------+-------+-------+  
   | name  |hobby1 |hobby2 |hobby3 |  
   +-------+-------+-------+-------+   
   | kris  | ball           


        

Answer 1

Your three-hobby table design probably violates what I usually call the spirit of the original 1NF (probably for the reasons given by dportas and others).

It turns out however, that it is extremely difficult to find [a set of] formal and precise "measurable" criteria that accurately express that original "spirit". That's what your other guy was trying to explain talking about "the ambiguity of repeating groups".

Stress "formal", "precise" and "measurable" here. Definitions for all other normal forms exist that satisfy "formal", "precise" and "measurable" (i.e. objectively observable). For 1NF it's just hard (/impossible ???) to do. If you want to see why, try this :

You stated that the question was "whether those three hobby columns constitute a repeating group". Answer this question with "yes", and then provide a rigorous formal underpinning for your answer.

You cannot just say "the column names are the same, except for the numbered suffix". Making a violation of such a rule objectively observable/measurable would require to enumerate all the possible ways of suffixing.

You cannot just say "swim, tennis" could equally well be "tennis, swim", because getting to know that for sure requires inspecting the external predicate of the table. If that is just "person has hobby and also has " , then indeed both are equally valid (aside : and due to the closed world assumption it would in fact require all possible permutations of the hobbies to be present in the table !!!). However, if that external predicate is "person spends the most time on and the least on ", then "swim, tennis" could NOT equally well be "tennis,swim". But how do you make such interpretations of the external predicate of the table objective (for ALL POSSIBLE PREDICATES) ???

etc. etc.