资料来源 : Free On-Line Dictionary of Computing

database normalisation
     
         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 into a separate table and connecting them with a
        {one-to-many relationship}.
     
        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://home.earthlink.net/~billkent/Doc/simple5.htm)}.
     
        [What about non-relational databases?]
     
        (1999-05-05)