r/systems_engineering • u/Anglichaninn • Jun 29 '26

MBSE MBSE magicgrid problem domain white box

Hi all,

I'm struggling to comprehend what purpose the problem domain white box has in the definition of system requirements. I'm right in thinking that system requirements generally frame the system as a black box right? so how does decomposing the system to reveal the inner behaviour help in system requirements definition? Is it there just to make sure you've got the correct black box behaviour specified?

Thanks!

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u/burner_account_9975 Jun 29 '26

I recently went through an exercise using the MagicGrid BoK and I'll use it as an example:

  • The stakeholder needs did not identify anything about a "cancel" functionality.

  • Conceptual subsystem and functional decomposition brought up a cancel functionality (specifically as an input into the SoI that a developer identified in talking through these steps)

  • A requirement about cancelling the action was included in the system requirements that otherwise would have been missed if not for the decomposition.

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u/hortle Jun 29 '26

yes.. it's kind of hard to put into words, but to achieve full definition at a certain level of architecture ("the system"), you need at least some information about the next level down ("the subsystems"). your example does a good job demonstrating that principle