- 2021-04-01 09:12
*views 10*- NF
- Database
- BCNF
- Knowledge accumulation

The first paradigm (1NF) Standard tables

The second paradigm (2NF) Partial functional dependency

The third paradigm (3NF) transfer function

BC normal form (BCNF) Candidate key correlation

The fourth paradigm (4NF) Eliminating multivalued dependencies

The fifth paradigm (5NF)

1NF The definition of

If the relationship model R Each attribute of is a data item that cannot be further divided , It is called relational pattern R Satisfy the first paradigm .

A relation in which that intersection of each row and column contains one and

only one value.

2NF The definition of

if R Satisfy the first paradigm , And every non principal attribute is completely dependent on the main code , be R Satisfying the second paradigm .

A relation that is in first normal form and every non-primary-key attribute

is fullyfunctionally dependent on the primary key.

3NF The definition of

if R Satisfying the second paradigm , And every non principal attribute does not depend on the main code , be R Satisfy the third paradigm .

A relation that is in first and second normal form , and in which no

non-primary-keyattribute is transitively dependent on the primary key

4 BC normal form （BCNF）

if R Satisfy the third paradigm , And each main attribute does not depend on the main code partially or transfer function , be R Satisfy the third paradigm .

Each attribute determines the set of attributes （ factor ） All include （ candidate ） code

R All properties in （ main , Non primary attribute ） All functions are completely code dependent

from BCNF Conclusion can be drawn from the definition of , A satisfaction BCNF What are the relationship patterns of ：

（1） All nonprimary properties are completely functional dependent on each code ;

（2） All of the main properties for each code that does not contain it , It is also a complete functional dependency ;

（3） No attribute is completely dependent on any set of attributes that are not codes .

A relation is in BCNF if and only if every determinant is a candidate key (we

identify all the determinants and make sure that they are candidate keys, )

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