Learn in the textbookE-R Diagrams, Key Design, and Normalization
DefinitionNormalization (正規化) is the design work of splitting one table into several to remove duplicated data and prevent inconsistencies when data is updated.
ExplanationWhen the same fact is stored in several places, a change may reach only some of them and leave the values out of step. Normalization splits tables according to which item each item depends on, then links the resulting tables through shared columns (primary and foreign keys). The further normalization goes, the finer the tables are divided.
AnalogyImagine a business partner's address that used to be copied onto every form, moved into a dedicated partner list so that forms carry only the list number. When the address changes, you fix one entry in the list.
Memory hookTo normalize is to put things into a standard form, and here tidying up has a counterintuitive effect: the tidier it gets, the more tables you have.