I will explain the relation (relation) between models.
The model can have relationships (relationships) such as 1: 1, 1: N.
The reference key (of the referencing model) is provided with "list box", "radio button", "check box", "search screen".
There is also a relation such as narrowing down by multiple reference keys.(Example: When selecting a large item, small items are narrowed down.)
In this chapter, we will explain references used in such general business matters.