database normalisation

1 definition found

database normalisation - Free On-line Dictionary of Computing (26 May 2007) :

  database normalisation
  1NF
  2NF
  3NF
  4NF
  5NF
  Codd's First Normal Form
  fifth normal form
  first normal form
  fourth normal form
  second normal form
  third normal form
  
     <database> A series of steps followed to obtain a database
     design that allows for efficient access and storage of data
     in a relational database.  These steps reduce data
     redundancy and the chances of data becoming inconsistent.
  
     A table in a relational database is said to be in normal
     form if it satisfies certain constraints.  Codd's original
     work defined three such forms but there are now five generally
     accepted steps of normalisation.  The output of the first step
     is called First Normal Form (1NF), the output of the second
     step is Second Normal Form (2NF), etc.
  
     First Normal Form eliminates repeating groups by putting
     each value of a multi-valued attribute into a new row.
  
     Second Normal Form eliminates functional dependencies on a
     partial key by putting the fields in a separate table from
     those that are dependent on the whole key.
  
     Third Normal Form eliminates functional dependencies on
     non-key fields by putting them in a separate table.  At this
     stage, all non-key fields are dependent on the key, the whole
     key and nothing but the key.
  
     Fourth Normal Form separates independent multi-valued facts
     stored in one table into separate tables.
  
     Fifth Normal Form breaks out data redundancy that is not
     covered by any of the previous normal forms.
  
     (http://bkent.net/Doc/simple5.htm).
  
     [What about non-relational databases?]
  
     (2005-07-28)