A recent course participant wrote to us with the following question:
In a Base Use Case “React to Threats to xx Platform”
Is the Primary Actor the Threat (Entity Role = Hostile)
OR
Is the Primary Actor some “xx “Platform
The Supporting Actors are given as Mission Operator, Flight Crew, Tactical Network and the actions are assumed to be taken by some “xx” platform to defend itself against an impending threat.
Answer:
What you are describing is commonly referred to as a misuse case: essentially a use case that represents a goal of a hostile actor.
And I would recommend applying the same use case heuristics that I taught in our training courses:
- Identify who the primary actor is—the one invoking the misuse case. (That would be the attacker, in this case).
- And then write the name of the use case—the verb phrase—from the perspective of that primary actor. (“Destroy platform,” for example.)
- When you write the Main Success Scenario for the misuse case, you are writing it from the perspective of that hostile primary actor. Completion of the Main Success Scenario is therefore good for that hostile primary actor and bad for the system you are designing. Your job as a design team is to then write the alternative branches off of that Main Success Scenario (i.e., the countermeasures) that would keep the Main Success Scenario from reaching its end.
The goal of writing out a narrative for a misuse case is the same as writing out a narrative for a use case: to derive additional functional and nonfunctional requirements that your system-of-interest must ultimately satisfy.
One final methodological tip: Some modelers like to color code use cases and misuse cases on their use case diagrams to visually distinguish the two sets.
I hope this was helpful.
