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  • 1. Requirements Development & Management Everything in its Place Levels, Allocation, and Traceability Lou Wheatcraft Compliance Automation, Inc. 1 Systems Engineering Engine Level n 2 NPR 7123.1A©Compliance Automation Inc.830/249-0308 2007
  • 2. Requirements Development & Management Requirements Hierarchy Direction Content Governing Approver Originator Document Needs, Goals, Agency strategic direction based on Strategic Plan Administrator Support Objectives higher-level direction and Strategic Organizations Planning Guidance Level 0 Agency Structure, relationships, principles Architectural Administrator Host MDAA Requirements governing design and evolution of Control with Inputs cross-Agency/Mission Directorate Document from Other systems linked in accomplishing (ACD) Affected Agency needs, goals, and objectives MDAAs Directorate High-level requirements levied on a PCA AA MDAA Requirements Program to carry out strategic and Level 1 architectural direction including programmatic direction for initiating specific projects Program Detailed requirements levied on a Program Plan MDAA Program Requirements Program to implement the PCA and Manager Level 2 high-level programmatic requirements allocated from the Program to its projects Detailed requirements levied on a Project Plan Program Project Project Project to implement the Program Manager Manager Requirements Plan and flow-down programmatic requirements allocated from the Program to the Project Level 3 System Detailed requirements allocated from System Project Responsible Requirements the Project to the next lower level of Requirements Manager System the Project Document Lead 3 3 NPR 7120.5D Levels – an illustration Super Science System Spacecraft System Mission Ops System Launch Vehicle Ground Support 4 System System©Compliance Automation Inc.830/249-0308 2007
  • 3. Requirements Development & Management Levels – Spacecraft System (product view) Spacecraft Level 3 System Level 4 ADC COM PWR GN&C RF Switch Transponder Antenna A Antenna B Level 5 ADC: Attitude Determination & Control Subsystem COM: Communications Subsystem PWR: Power Generation, Distribution, and Control Subsystem GNC: Guidance Navigation, & Control Subsystem 5 Common Level Problems • Requirements at the wrong level • Higher-level requirements not implemented at lower levels • Lower-level requirements that cannot be justified by higher-level requirements • Inadequate impact assessment of changes to requirements Allocation and Traceability can help you identify and correct these problems 6©Compliance Automation Inc.830/249-0308 2007
  • 4. Requirements Development & Management Allocation Defined Allocation is the process by which requirements, defined at one level are assigned to the parts of the architecture at the next lower level 7 What is being allocated? • Requirements – Functional – Performance – Operations, – -ilities, – Design and Construction Standards • Resources – Mass, Volume, Power – Cost, Schedule 8©Compliance Automation Inc.830/249-0308 2007
  • 5. Requirements Development & Management S/C System Allocation E A B C F Spec 9 Allocation E A B C F S/C System Spec S/C System Architecture COM ADC Subsystem Subsystem From system requirements we create an architecture 10©Compliance Automation Inc.830/249-0308 2007
  • 6. Requirements Development & Management Allocation E A B C F S/C System Spec S/C System Allocate Architecture Requirement to Part A B C ADC Subsystem COM Subsystem Then we can allocate to the next level Requirements ABC are allocated to the Communications Subsystem 11 Allocation E A B C F S/C System SRD S/C System Architecture A B C AD&C Subsystem COM Subsystem COM 1 2 3 4 5 Subsystem Spec Comm Subsystem Architecture Antenna RF Switch Antenna A B Transponder 12©Compliance Automation Inc.830/249-0308 2007
  • 7. Requirements Development & Management Repeat Allocation Process at Each Level Requirements Architecture and Design Allocate requirement to next level 13 How to do Allocation • Create an allocation field as an attribute of each requirement in your RM tool • Allocate requirements to the next level architecture when you have a good draft baseline of requirements • Generate allocation matrix to evaluate the completeness of your requirements • Create reports to help – Assess requirements during development – Manage change 14 Customer-Centered Products, p. 151©Compliance Automation Inc.830/249-0308 2007
  • 8. Requirements Development & Management Ensure Every Requirement Allocated S/C System Requirement Allocation Matrix (RAM) Requirement COM ADC GNC PWR Total SC1: Requirement Text 1 1 SC2: Requirement Text 1 1 2 SC3: Requirement Text 1 1 1 3 SC4: Requirement Text 0 • Generate allocation matrix • Assess totals – SC4 not allocated – SC1 assigned to a single element, • May not be system level requirement • May not be properly allocated to the other subsystems • Resolve problems 15 Analyze Correctness of Allocation S/C System Allocation to COM Subsystem Matrix Requirement COM ADC GNC PWR Total SC1: Requirement Text 1 1 SC3: Requirement Text 1 1 1 3 S/C System Allocation to not-COM Matrix Requirement COM ADC GNC PWR Total SC2: Requirement Text 1 1 2 SC4: Requirement Text 0 • List elements allocated to Communications Subsystem • List elements not allocated to Communications Subsystem • Analyze to determine if allocations are correct • Ensure requirements are in proper sections of the System Specification 16©Compliance Automation Inc.830/249-0308 2007
  • 9. Requirements Development & Management Looking for Interfaces S/C System Requirement Allocation Matrix Requirement COM ADC GNC PWR Total SC1: Requirement Text 1 1 SC3: Requirement Text 1 1 1 3 • SC3 is allocated to COM, ADC and PWR – May indicate an interface – Cross check with SE architecture model • Allocation matrices needs to mirror SE Model generated data 17 Looking for Interfaces (2) • Some Spacecraft requirements will be allocated to multiple subsystems but there is no physical interface – [SC12] The Spacecraft shall have a 10-year on-orbit lifetime – [SC15] The Spacecraft shall have an on-orbit mass of less than 5,000 lbm. • These are “Resource” allocations 18©Compliance Automation Inc.830/249-0308 2007
  • 10. Requirements Development & Management Do’s and Don’ts of Allocation • Do allocation in a timely manner • Do allocation in conjunction with other good system engineering practices • Do use allocation matrices, in conjunction with traceability matrices, to examine how well you have allocated and also the quality and coverage of your requirements • Do not write element requirements as a way to accomplish allocation 19 Traceability Defined Traceability is the process of linking a lower level requirement back to its source requirement. 20©Compliance Automation Inc.830/249-0308 2007
  • 11. Requirements Development & Management Traceability E A B C F S/C System Spec A B C TRACE Requirement to Requirement Communications 1 2 3 4 5 Subsystem Spec Traceability along with Allocation quickly shows us possible problems 21 Customer-Centered Products, p. 151 How to do Traceability • Create trace as an attribute that must be supplied with requirement if not going directly into an RM tool • Add trace linkages when entering requirement into RM tool • Generate traceability matrix • Create reports that shows child - parent and parent – child linkage – Ensure all children traced to a parent – Ensure all children traced to proper parent – Ensure all parents have children 22©Compliance Automation Inc.830/249-0308 2007
  • 12. Requirements Development & Management Ensure Allocation and Traceability • Provide each subsystem a Spacecraft requirement allocation matrix of its allocated requirements • Subsystem requirement writers will trace their derived requirements to the Spacecraft requirements allocated to them • Use RM tool to maintain traceability • Use RM tool to generate allocation and traceability matrices and other reports needed to assess and manage requirements 23 Spacecraft Requirement with No Child • Create a report showing Spacecraft requirements allocated to a subsystem that have no subsystem children (derived requirements) • Possible problems and solutions – Child requirements were not traced correctly – fix the link – The System requirement was incorrectly allocated – fix the allocation – No child has been written but is needed – fix the Element requirements • Create a report and analyze problems frequently 24©Compliance Automation Inc.830/249-0308 2007
  • 13. Requirements Development & Management Subsystem Requirement with Suspect Parent Report showing Subsystem Child traced to non-allocated Parent COM (child) COM (child) S/C System (parent) S/C System Requirement Rationale Requirement (parent) (not allocated to COM) Rationale COM_14 Text COM_14 SC1 Text SC1 Rationale Rationale COM_234 COM_234 SC23 Text SC23 Text Rationale Rationale • Possible problem and solutions – Incorrect linkage made – fix the linkages – A requirement was not allocated to COM Subsystem that really should have been – fix the allocation – The lower level requirement is incorrect and has no reason to exist – get rid of the lower level requirement • Create report and analyze problems frequently 25 Quality of Child Requirements System Requirements with Problem Children Allocated S/C S/C COM (child) COM ADC (child) ADC Etc. (parent) Reqmt Rationale Requirement Rationale Requirement Rationale SC3 Text Rationale COM_35 Text Rationale ADC_14 Text Rationale ADC_45 Text Rationale SC15 Text Rationale COM_23 Text Rationale ADC_16 Text Rationale ??? COM_87 Text missing • Analyze the traced requirements and their rationale – How much is traced and what is missing – Is the child text consistent with the parent – Does the rationale make sense and is it consistent • May be sorted in parent requirement ID order or the order they appear in the S/C system spec 26©Compliance Automation Inc.830/249-0308 2007
  • 14. Requirements Development & Management Do’s and Don’ts of Traceability • Do traceability as requirement is written • Do traceability in conjunction with other good system engineering practices • Do use traceability matrices, in conjunction with allocation matrices, to make sure the requirements trace to the proper parent • Do not trace a requirement arbitrarily 27 Allocation and Traceability -- the Requirement Definition Process • Define scope – Need, Goals, Objectives – Stakeholders – includes owners of parent requirements – Drivers – includes allocated requirements – Operational Concepts – Identify External Interfaces • Perform functional and engineering analysis • Define the interfaces • Write requirements (trace each to a parent requirement) – Requirements addressing requirements allocated to your system – Requirements addressing drivers and constraints • Perform functional and engineering analysis • Define architecture • Allocate requirements to architectural elements at the next level • Repeat entire process for each element at the next level 28©Compliance Automation Inc.830/249-0308 2007
  • 15. Requirements Development & Management Combine Allocation and Traceability to Uncover Possible Requirement Defects • Requirements not allocated • Requirements not allocated correctly • Requirements without parents • Requirements with incorrect parents • Requirements with incorrect children • Child requirements are not necessary or are not sufficient to implement the parent requirement • Interfaces are not addressed 29©Compliance Automation Inc.830/249-0308 2007