Mission, Capabilities and Functions

Arcadia
1

Hi,
I wanted to use Capella to demonstrate the consistency between system’s missions, its capabilities and its functions.
I depicted the missions and capabilities using the MCB diagram, and mapped (capability exploitation) between them.
Few questions:

  1. I wanted to associate them with the system, but couldn’t find how to do that. Any advice?
    Since I could not do it, I created the only system related element which appears in the MCB diagram: Actor. I associated the specific actor with both the missions and the capabilities (using “involved actor”).
  2. I then wanted to show how the system functions (or at least functions implemented by the actor) related to the required capabilities. I could not find any diagram to do so. I could only find the SAB diagram to create the system functions, but could not find how to allocate them to the agent nor could I relate them to any capabilities. Any advice?
    Thanks,
    Avi
2

Hi Avi,

  1. The MCB is at the System Analysis level in Capella. this means that all missions and capabilities you created are System Mission and System Capabilities by definition, hence they are associated with the system just by the fact that they exist. I don’t think this is a good idea to create a System Actor, the System component already exists at the system analysis level (as a System Component - black box)
  2. Yes, a couple of advice:
  • First of all, Capabilities are described by Functional Chains and Scenarios (they are themselves made of Functions and Functional exchanges) - here is an overview of this:
    https://www.youtube.com/watch?v=BtzhlZUaWA8&t=87s
  • There are quite a lot of diagrams where you can create functions: SFB, SDFB, FS… but SAB would work as well - Are you using the Activity explorer? There is a specific entry on it for creating/managing system functions at the System Analysis level
  • The questions you are asking makes me think that you may want to start by going through this tutorial:
    https://esd.sutd.edu.sg/40014-capella-tutorial/ it should help you better understand that Arcadia concepts and approach.
    I hope this helps.
    Stephane
3

Thank you Stephane. I looked into the material you mentioned.
I now understand the implicit relation between a system and missions / components. However, I do wish to express it explicitly in a diagram (for communication with stakeholders). This is a gap.
Additionally, according the popular definitions, functions help to achieve capabilities, and are not necessarily a component of a capability. Functions (as system characteristics) enable the capability (an actor characteristic).
I suspect there is a gap in Arcadia with respect to this perception.
Regardless, how do I create a functional chain diagram to describe a capability with a functional chain? Could not find it in the tutorial (I guess because it’s a new feature).
Thanks in advance!
Regards,
Avi

4

Hi Avi,
I did not say that Functions are a component of a Capability, I said they are used to describe them, and indeed in Arcadia Functions helps to achieve Capabilities, so I think we are aligned here.
If you want to communicate to stakeholders that Capabilities are System Capabilities, you can use a Note in your diagram.
There are different ways to create Functional Chains in Capella, and this is not a new feature. It is covered in the tutorial, for exemple here:
https://esd.sutd.edu.sg/40014-capella-tutorial/SystemAnalysis.html#Chain but you can also read the embedded Capella documentation I guess.
Stephane

5

Thank for the pointer. Sorry I missed it.
However, I am still missing the explicit relationship (also between capability and function). I will look into this more thoroughly though.
Best regards,
Avi

6

First of all about capabilities. You can manipulate Capabilities in the 4 engineering perspectives (OA/SA/LA/PA) but they have different meanings depending on which perspective you are.
System Capabilities you have created are by definition Capabilities of the System, and as they are on the SA, they are expressing the need.
At the LA/PA level, they are Capability Realisations, so expressing the solution.
If you want to explicitly show you that they are System Capabilities, please find attached an example of how to do it using a Note.
Also, about linking Capabilities with Functions: There is an “Involved System Functions” relation between Capabilities and Functions. This relation is automatically calculated based on the Function Scenario or Functional Chains you create under a Capability (but you can also manually enter functions here using the property tab).
This relation is easily seen using the semantic browser on a Capability (see the example attached).
I hope this helps.
Stephane

[MCB] System Missions and Capabilities.jpg
Semantic browser.png
[MCB] System Missions and Capabilities.jpg
Semantic browser.png

7

That’s very helpful Stephane.
I will try to prepare something and maybe continue the discussion here with a meaningful example.
Thanks!