Database Administrators Stack Exchange is a question and answer site for database professionals who wish to improve their database skills and learn from others in the community. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

A normalized relation can still suffer anomalies. Going the other way, which (if any) normal forms can be violated by a relation that's free from anomalies? If such exist,

  • For each such normal form that can be violated, what is an example of an anomaly free relation that violates the normal form?
  • Are there any normal forms that an anomaly free relation is guaranteed to comply with?
share|improve this question
If "all normal forms" includes DKNF then the answer is no. A relation in 6NF does not have undesirable update, insertion or deletion anomalies in the usual sense but it still may not satisfy DKNF. On the other hand DKNF is not very important and is frequently irrelevant or unachievable. – sqlvogel Jan 25 '12 at 6:47
@sqlvogel: hopefully the edit resolves the ambiguity. Interestingly, one of the schema that inspired this question is (as far as I can tell) valid 6NF but not DKNF. I'm not confident enough in my knowledge of normal forms to say with certainty if this is an example that fulfills parts of my question. – outis Jan 25 '12 at 7:53
Consider whether the set 'update anomalies removed by normalization' is a subset of 'update anomalies'. – onedaywhen Jan 25 '12 at 8:48
@onedaywhen: If A is the set of relations with anomalies (not exactly the set of update anomalies, but...) and N the set of normalized relations, then the former is A-N, which is naturally a subset of A (is that what you were getting at?). However, I'm asking about neither anomalous, non-normalized relations nor anomalous, normalized relations (A ∩ N). I'm asking about the non-anomalous, non-normalized relations (which involves the complement of update anomalies); whether A̅ ∩ N̅ is empty and, if not, what are some example elements. – outis Jan 25 '12 at 9:31
If you are using the word "anomalies" to refer to anything other than "update anomalies" (where the word "update" means assignment i.e. insert, amend and delete operations) then please define it. Also, "normalized" means 1NF and is a fundamental requirement of the relational model, hence "non-normalized relations" is a contradiction. If you are referring to something that isn't a relation then, again, please define it. – onedaywhen Jan 25 '12 at 11:43

A relvar that is considered free of all update anomalies will satisfy 6NF and by implication 5NF and BCNF (other normal forms defined many years ago are no longer deemed useful).

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.