System of Interest

I am tyring to model an Adaptive Cruise Control system. Following the Arcadia methodology, I am not including the ACC system as my entity in OA. So I modeled a ‘Vehicle System’ entity that would represent my expected activities for my capabilities. Now when I go to the System Analysis phase, I get a block for my system, which I have to name ‘ACC system’ as it is my ‘System of interest’. I also have a System Actor for the ‘Vehicle System’ transitioned from the previous phase.
Now I am confused about the following:
My ‘ACC System’ system block would involve all the sensing and decision making functions whereas the ‘Vehicle System’ would have all the actuating and HMI functions. However, because of my OA, I now have functional exchanges between the ‘Driver’ and the ‘Vehicle System’. For example, Set Desired Speed’ (Driver) >> ‘Maintain Speed’ (Vehicle System). At this stage, I moved the functions relevant to ACC from ‘Vehicle System’ to ‘ACC System’. As I now have functional exchanges between ‘Driver’ and ‘ACC System’, I will have to create a component exchange between ‘Driver’ and the ‘ACC System’ to allocate these functional exchanges to. However, this would not be feasible as the driver would not be interacting with the ACC System per se but with the Vehicle Control Switches in the ‘Vehicle System’ that are actually sending the commands to the ACC System (which I will define in my logical phase I guess?). But my [SAB] says something else. What should I do now?
Should I create a new function in the Vehicle System for monitoring cruise control inputs and then from there to ACC System? Or should change the ‘System of Interest’ completely to something like ‘ACC Equipped Vehicle’?
Also, the ‘ACC System’ will be a part of the ‘Vehicle System’. So is this the right approach to model ACC. Am I misinterpreting some concepts here?

If I understood well (a diagram could have helped me
), this is a good example of the added-value of Operational Analysis (OA).
In your case, the ‘Maintain Speed’ in OA (allocated to Vehicle System) will be certainly PARTLY realized by the ACC system. You will need to define, along with the Vehicle System designers, the scope of responsibility : as a minimum, as the ACC has no direct interface with the Driver, the Vehicle System will at least ensure this interface (but I guess it will be more complicated than that). And this shall be done from System Needs Analysis perspective, but can be detailed at Logical Architecture and beyond.
Regarding the position of your ACC wrt the Vehicle System : indeed, if you are the Vehicle architect, you will consider that the ACC is part of the Vehicle. But if you are the ACC architect (and hence the ACC is your System Of Interest), the Vehicle infrastructure will be an external actor to you, because you don’t have control over it and still you are interested in the interfaces between ACC and Vehicle.
Hope it helps.

to complement Juan answer:
in Arcadia, each operational activity in Operational Analysis (OA) is expected to be “supported” by some system functions that are expected to contribute to this activity, along with external actors or systems that will take their part of this activity.
Therefore, the tooled transition as offered by Capella should only be considered as a way to initialise the System Need Analysis (SA), and as a reminder of OA, to be turned into expectations on the system and its interfaces with external actors.
So the single SA function resulting from transition of the OA activity is not to be taken as is, in most cases. If you have some trouble in allocating it either to ACC system or external actors, then it is likely that you should replace it by several others. Be prepared to create several functions for each operational activity (if relevant), and allocate them to either the ACC system (e.g. here sensing and decision making functions), or other vehicle subsystems, including HMI (e.g. ‘Set Desired Speed’). Then you will create traceability links between each of these functions and the activity they contribute to.
Does this help ?

Hi Juan and Jean-Luc,
Thanks for your responses. Your responses definitely helped. I am indeed modeling from the perspective of an ACC Architect, hence the vehicle subsystems were not of my concern. However, during the Physical Architecture phase, I have defined physical components of the actuating and HMI subsystems in the ‘Vehicle System’ actor to define the interfaces.