The third post focused on the second normal form, its definition, and examples to hammer it home. Once a table is in second normal form, we are guaranteed that every column is dependent on the primary key, or as I like to say, the table serves a single purpose.
Elementary key normal form (EKNF) is a subtle enhancement on third normal form, thus EKNF tables are in 3NF by definition. This happens when there is more than one unique compound key and they overlap. Such cases can cause redundant information in the overlapping column(s).
and join dependencies. ETNF lies strictly between fourth normal form and fth normal form (5NF, also known as projection-join normal form). We show that ETNF, al-though strictly weaker than 5NF, is exactly as e ective as 5NF in eliminating redundancy of tuples. Our de nition of ETNF is semantic, in that it is de ned in terms of tuple redundancy.
Un-Normalised Form (UNF) To produce the Un-Normalised Form (UNF)of an entity we must: list the attributes of the entity; identify the main key; identity the repeating group of attributes; identify its key; We carry out the process using a special document, as shown below.