Third Normal Form

Functional Dependency

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USEFULL FOR FYBSC (IT) & TYBSC (CS) STUDENTS

 

·         In the process of efficiently storing data, and eliminating redundancy, tables in a database are designed and created to be in one of five possible normal forms.  Each normal form contains and enforces the rules of the previous form, and, in turn, applies some stricter rules on the design of tables.·         A set of tables in a database are initially said to be in 0 normal form. First Normal Form:

  • Tables are said to be in first normal form when:-
  • The table has a primary key.-
  • No single attribute (column) has multiple values.-
  • The non-key attributes (columns) depend on the primary key.
  • Some examples of placing a table in first normal form are:

2

In first normal form the table : –

4

 

Second Normal Form:

  • Tables are said to be in second normal form when:
  • o   The tables meet the criteria for first normal form.
  • If the primary key is a composite of attributes (contains multiple columns), the non key attributes (columns) must depend on the whole key.
  • Third Normal Form:
  •  Tables are said to be in third normal form when:
  • o   The tables meet the criteria for second normal form.
  • o   Each non-key attribute in a row does not depend on the entry in another key column. Fourth
  • Normal Form:
  • Tables are said to be in fourth normal form when:
  • o  The table meets the criteria for third normal form.
  •  Situations where non-key attributes depend on the key column exclusive of other non-key columns are eliminated. Fifth Normal
  • Form:
  • Tables are said to be in fifth normal form when:
  • o The table meets the criteria for fourth normal form.
  • o The table consists of a key attribute and a non-key attribute only.

 

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