Fifth normal form (5NF), Sixth normal form (6NF) - Databases: design

The fifth normal form (5NF)

Often there is a dependence of the attributes of a relationship when they are pairwise dependent on each other. For example, a relationship with the attributes Order & quot ;, Goods & quot ;, Supplier is such because there is a functional dependence of the goods on the supplier, as well as the dependence of the order on the goods and the supplier. This functional relationship is called the dependency of the connection. It can be defined in the following way: the order contains many goods, the goods are supplied by a multitude of suppliers, the supplier is contained in a variety of orders.

Considering the fifth normal form, it is necessary to remember that for this solution there must be at least one potential key that will allow dividing the relationship into two relations without loss of data.

The ratio is in the fifth normal form if and only if it is in 4NF and each non-trivial dependence is determined by its potential key.

Thus, the relationship in question is not in 51IP, because the data instance is not determined by the potential key Order and (or) "Item", but is formed only by a combination of all the attributes of the relationship. As a result, the original ratio can be divided into three relations that will be in the fifth normal form (Figure 2.84).

Fig. 2.84. Representation of the ratio in 5NF

The

This separation leads to the formation of dependencies from potential keys in each relation, and the connection of relations will form a completely accurate initial ratio.

The 4NF transition rule is 5NF

If the ratio is in 4NF and there are dependencies of the connection that are not determined by the potential keys, then the relationships containing such dependencies are distinguished.

As a result of all normalization operations up to 5NF, it is considered that the developer receives a fully normalized relationship, containing no update anomalies.

Sixth normal form (6NF)

Sometimes in databases you need to use chronological information that obeys the time data, where one of the attributes is a date and/or time, or an interval value, because the chronology can be reflected not only by time data, but also by other elements that can be represented in form strictly in sequence and express a range of values. The use of temporary data is due to the need to reflect in the database the chronology of the life of certain information or a combination of them. For example, in time you can track the status of an order, entering an order in the order or something else. In this case, each time tracking element is subject to its own time indicator. As a result, the relation must have its own instance for each change of the tracking attribute (Table 2.26).

Table 2.26

Sample Order Order

Order

Status

Product

Date

31

Created

-

01/01/2014

31

Created

Vacuum cleaner

01/01/2014

31

Created

Vacuum cleaner, teapot

02/01/2014

31

Designed

Vacuum cleaner, teapot

02/01/2014

31

Paid

Vacuum cleaner, teapot

03/01/2014

31

Delivered

Vacuum cleaner, teapot

01/06/2014

The

The

Of course, this attitude is problematic enough to handle, because you need to duplicate previously generated information, and there are anomalies of updates that require monitoring of existing data.

The ratio is in the sixth normal form if and only if it is represented in 5NF. satisfies all non-trivial dependencies of the connection, and one of the projections under consideration is satisfied for all the attributes of the relation.

In fact, the ratio in the sixth normal form implies the allocation of the relationship, but to the temporary linked potential key and the relationships in the attributes subject to chronology with this potential key (Figure 2.85).

Fig. 2.85. The ratio of 6NF

The

5NF 6NF transition rule

If the ratio is in 5NF and there are time-independent chronological attributes, then the chronology ratio that makes up the temporary development is distinguished with the attributes in the form of a key that is used in the allocated relations according to the chronological attributes functionally dependent on the temporary key.

This migration procedure allows you to solve the problem of fixing the life of each attribute, which depends on the time and provides the necessary data integrity.

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