Systems Engineering ‘in the small’

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In software engineering, you can think of two levels: micro-level and macro-level.  On the micro-level, this is systems engineering ‘in the small.’  On the macro-level, there’s systems engineering ‘in the large.’  The two levels are complimentary. In Scenarios, Stories, Use Cases: Through the Systems Development Life-Cycle, Ian F. Alexander and Neil Maiden write about systems engineering ‘in the small.’ 

Systems Engineering ‘In the small’ Activities

Alexander and Maiden identify the following systems engineering ‘in the small’ activities:

  • User Requirements Definition (URD)
  • System Requirements Definition (SRD)
  • System Design / Architecture (SD/A)
  • Preliminary Design (PD)
  • Detailed Design (DD)
  • Implementation (Imp)
  • Test and Integration (T&I)
  • Acceptance and Certification (A&C)

Systems Engineering ‘In the small’ Activities Explained

Alexander and Maiden explain the key systems engineering ‘in the small’ activities as follows:

  • User Requirements Definition (URD) – The process of finding out who the users are, what they do, and what their needs are.
  • System Requirements Definition (SRD) – The process of finding the constraints  that have to be applied to the system acquisition process to obtain a fit-for-purpose result.  The system constraints can include detailed functional behavior, legislation, regulations, standards, technical interfaces, environmental and physical.
  • System Design / Architecture (SD/A) – The overall shape of a compliant solution is worked out.  Principal subsystems are identified and their individual requirements flowed down and refined.
  • Preliminary Design (PD) – Carry out sufficient design to provide confidence that the flowed-down system requirements are achievable at subsystem level.  It often concludes with a Preliminary Design Review (PDR).
  • Detailed Design (DD) – Carry out sufficient design to support implementation.  It should provide confidence that subsystem flowed-down requirements will be met.  This activity should be concluded with a Critical Design Review (CDR).
  • Implementation (Imp) – Here the subsystem designs are implemented using the relevant technologies, and tested at subsystem level.  Testing should determine that flowed-down requirements have been met.
  • Test and Integration (T&I) – During this activity, the individual components come together for testing as an integrated whole.  Compliance with the user and system requirements should be demonstrated.
  • Acceptance and Certification (A&C) – This activity is when the user community or their representatives take a tested and integrated system and confirm that what has been built is indeed what was wanted.  In highly regulated and/or high-integrity applications, this will involve approval by the appropriate certifying bodies.

Key Take Aways

Here’s my key take aways:

  • ‘in the small’ activities is micro-level systems engineering whereas ‘in the large’ is macro-level systems engineering.
  • Systems engineering ‘in the small’ and systems engineering ‘in the large’ are complimentary.
  • Systems engineering ‘in the small’ activities fit within systems engineering ‘in the large’ activities and phases.
  • Systems engineering ‘in the small’ activities include: User Requirements Definition, System Requirements Definition , System Design/Architecture, Preliminary Design , Detailed Design , Implementation, Test and Integration , Acceptance and Certification

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