Rules of Fourth Normal Form
1. One key value determines one tuple with all its attributes.
2. The existence of the relation implies a functional dependence between each key and its attributes.
3. The relation is represented as a flat table, where each tuple is a row and each type of attribute occupies a given column; there is only one element per row.
4. All tuples have the same contents; the same attributes in the same order.
5. Each key and each tuple is unique; the relation is a set.
6. When a key is made of several attributes, a given nonkey attribute is determined by the entire key.
7. An attribute is determined by no other attribute but the key.
8. In a given tuple, all attributes have a value.
9. A relation comprises at least one key attribute and one other attribute.
10.When the key of a relation comprises several attributes, these attributes are mutually independent.