The normal forms from 1NF and upwards have well known definitions in papers by Codd and others.
I have sometimes seen the term 0NF or zeroth normal form used for a data set which is not in first normal form, but the definition seem to vary. Two definitions I have seen:
- A data set which cannot be viewed as a valid relation, e.g. no primary key, duplicates, varying number of columns.
- A valid relation (primary key, no duplicates, unambiguous column names and so forth) which is not in first normal form due to non-simple domains on some attributes.
Is there some commonly accepted definition, or is 0NF just an imprecise term?