Variant Configuration - Dependency Type

In SAP system, there existed three kinds of Dependency Types: Precondition / Procedure (Action) / Selection Condition.
What's the difference between them and What's the application area about them each other?

Difference:
Example 1: Precondition
Chars 2 only appear if Char 1 has values such as following picture:
If the Char 1 has no value. (before)

After input value to Char 1.


Operation Guide:
T-code: CT04 - Change Chars 2, Click menu: Extras->Object Dependency->Editor.
Select Precondition, in Line: 000010, input: TX100 SPECIFIED.

Example 2: Procedure (Action)
Chars 1 value decided the default Value of Chars 2.
If I select SUNBURN-1000 for Chars 1, the Chars 2 will has an default value
inputed by system automatically. Like following:


Operation Guide:
T-code: CT04 - Change Chars 1, Click menu: Extras->Object Dependency->Editor.
Select Procedure, in Line: 000010, input: $self.TX200 = 'CRUISER'.

Example 2: Selection Condition
If Char2.value has been assigned 'SUPERSPORT', an entry is required for Chars3.


Operation Guide:
T-code: CT04 - Change Chars 3, Click menu: Extras->Object Dependency->Editor.
Select Selection Condition, in Line: 000010, input: $self.TX200 = 'SUPERSPORT'.
Note:
If the char 2 has the value: supersport and you didn't maintain any value to Char 3.
System will pop up message to inform you that you haven't input value for char 3.

Application Area:
Precondition: Characteristic (Basic Data) / Characteristic Value
Selection Condition: Characteristic (Basic Data)
Procedure (Action): Characteristic (Basic Data) / Characteristic Value / Class

Of course, Above is just some simple samples for you to know about the topic of Dependency Type. The most widely usage of Dependency Type is to Link the Characteristics value to Actual component.

Following I will continue to talk about that topic.