I don't think I fully understood your question.
When multiple servers provide a service, the impact model is used to control it. There you define the impact of a server failure.
If you have three servers:
3 up and running - green
2 up and running, 1 down - green or yellow
1 up and running, 2 down - yellow or red
3 down - dark red
This is a feature of the impact model and does not depend on the relationship.
thank you for your answer .
What i mean is jus if 3 B are down so A is Down. How i can represent this situation in impact relation?
Which kind of relation i have to use?
If I understood your scenaria correctly at high level you are looking for below:
1. If class A is impacted then class B is Impacted. A=>B
2. If Class B (All CIs) is impacted class A is impacted. B=>A
It will result into a Cyclic Impact flow situation and hence, it may not work the way you want. The impact should flow only in one direction parent => child not the other way around.
If you could share the actual problem statement, may be we could think of a solution.
is no all B but just 3-4 (B1,B2,B3)of them if they are impacted 1 A (f exp. A1) is impacted