Data Normalization

1.Why Data Normalization?

The advantage of having a higly normalized data schema is that information is stored in one place and one place only, reducing

the possibility of inconsistent data. Furthermore, highly normalized data schemas in general are closer conceptually to

object-oriented schemas because the object-oriented goals of promoting high cohension and loose coupling between classes

results in similar solutions. This generally makes it easier to map your objects to your data schema.

cohesion:n. 凝聚，内聚

 

First Normal form(1NF): An entity type is in 1NF when it contains no repeating groups of data.

Second Normal form(2NF): An entity type is in 2NF when it is in 1NF and when all of its nonkey attributes are

fully dependent on its primary key.

Third Nomal form(3NF): An entity type is 3NF when it is in 2NF and when all of its attributes are directly

dependent on the primary key.