Normal Forms
© Copyright Frank D. Kanu 2000-2008
There are a few ways of describing normal forms out there.
Some have 5 normal forms, some 4.
Some count Boyce-Codd in and some don’t.
Here is one of the definitions I use quite often:
First normal form (1NF) - basics of organized data
Sidetrack:
Primary keys
Second normal form (2NF) - removing duplicative data
Third normal form (3NF)
Fourth normal form (4NF)
Technorati (All Links are external): atomic values attributes boyce codd definitions dependencies dependent duplicates entities fourth normal form primary key primary keys programmers rdbms separate tables sidetrack stable subsets it
There are a few ways of describing normal forms out there.
Some have 5 normal forms, some 4.
Some count Boyce-Codd in and some don’t.
Here is one of the definitions I use quite often:
First normal form (1NF) - basics of organized data
- The attributes of a relation should only contain atomic values - with other words eliminate duplicative columns from the same table.
- Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
Sidetrack:
Logical keys
A logical key is combined of attributes. It is used to avoid duplicates in the database.
Primary keys
The primary key is nothing else then a physical unique identifier for every single row. Most RDBMs have this key implemented for internal use, but not available for the programmers use.
The primary key has to be stable. With other words it can NEVER be changed.
The primary key must never be the same as the logical key, because the logical key is made up by entities which values can change.
Second normal form (2NF) - removing duplicative data
- The relation must be in 1NF
- All non-key attributes must depend on the primary key.
(Move subsets of data to their own tables)
Third normal form (3NF)
- Meet the requirements of 1NF and 2NF
- Remove columns that are not fully dependent upon the primary key.
(All non-key attributes shall depend on key attributes.)
Fourth normal form (4NF)
- Meet the requirements of 1NF, 2NF and 3NF
- A relation is in 4NF if it has no multi-valued dependencies.
Tags:
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