From database diagram to relational representation ¶

Rule 1: a class translates to a relation ¶

The class below:

Correspond to the relation:

Agent(name: String, #secretCode: String, age: int)
Unit(#name: String, location: String)

Rule 2: n..* to m..* relationships ¶

The association Belong below:

Correspond to the relation:

Belong(#unitName=>Unit.name, #secretCode=>Agent.secretCode, years: int)

And the constraint (as there is a 1..*):

secretCode IN Belong

➡️ An alternative syntax for primary keys is #unitName=>Unit(name).

Rule 3: n..* to 0..1 or 1 relationships ¶

The association Belong below:

Correspond to the relation:

Agent(name: String, #secretCode: String, #unitName: Unit.name, years: int)
Unit(#name: String, location: String)

Unit in Agent

What rules to apply?

• Given A(0..1) and B(???), the identifier is A is added in B (🔄️)
• Given A(1) and B(???), the identifier of A in B is NOT NULL (🔄️)
• Given A(???) and B(1..*), every identifier in A must appear in B at least once(🔄️)
• The association class goes to the side with n..*

Rule 4: 1 or 0..1 to 0..1 or 1 relationships ¶

Missing.

Rule 5: self relationships ¶

A self-relationship is the same as a relationship between two classes. Refer to rules 2 to 4.

Rule 6: generalizations ¶

Missing.

Rule 7: n-ary associations ¶

Missing.