System Engineering Management Plan
Section 4.2 - Model Text

4.2 Functional analysis.

Functional characteristics shall include general and detailed requirements under appropriate sub-headings for all performance requirements, i.e., what is expected of the system, item, or material. In general both upper and lower performance limits shall be given.
This paragraph should include:

• dynamic characteristics (e.g., Rates, velocities, movements, etc.);
• quantitative criteria for the equipment under stipulated environmental and other conditions (e.g., range of output performance parameters with associated input parameters);
• qualitative characteristics.

Where appropriate, performance acceptance limits should be specified.

System capabilities and the states and modes of the system shall be progressively identified and analyzed as the basis for identifying alternatives for meeting system performance and design requirements.
The system capabilities used include mission, test, production, deployment, and support functions.
The performance characteristics and their states and modes of the system shall be developed in an iterative way based on the results of the mission analysis, the derived system performance requirements, and the synthesis of the lower elements.
System requirements shall be established for each performance characteristic specified by system capabilities in the context of states in which the system can exist and the modes of operation within each state.
When time is critical to a system requirement or performance characteristic, a time line analysis shall be made.
The specifications shall be prepared using the 'Documentation Standard' and shall be used to specify requirements for the preparation of performance specifications and detailed specifications.
The format and content of the System Specification shall be in accordance with the System/Subsystem Specification model text.

• 4.2.1 Functional analysis procedure.
• The top-level functions identified from the mission analysis include the actions, and sequence of actions, required for the system (user, hardware, software) to complete each mission phase.
  The functions will be iteratively analyzed to lower levels of specificity. System functions will be assessed and criteria developed, based on human and machine capabilities and limitations, to determine which should be manual, and which should require an interaction between user and software.
  Alternatively, a 'Value Engineering Program Plan' can be implemented for any system where an analysis of its function is required for re-engineering purposes.
  
• 4.2.2 Value engineering.
• Value Engineering is a technical effort to obtain an optimum value by providing the necessary function at the lowest life cycle cost. Usually performed as a re-engineering task on an existing system or subsystem.
  
  • Value engineering analyzes equipment by function rather than by hardware and software a seeks to reduce cost of the function.
  • Value engineering employs the application of a job plan which includes the following steps:
    1. Information gathering;
    2. Definition of function;
    3. Speculation on alternatives;
    4. Evaluation of all alternative ways of meeting the requirements;
    5. Verification;
    6. Presentation of proposals;
    7. Implementation and follow up.
       
• Under construction.
  
• 4.2.3 System design.

• The system shall be partitioned into subsystems. The subsystems shall be partitioned into CSCIs, HWCIs, and equipment taking into consideration the maintainability policy.
  The design of subsystems shall include considerations for re-usability for any future projects. When subsystems are re-engineered they shall be designed so that they are reusable and maximize the use if existing, particularly commercially available products.
  The decision to make or buy the subsystems shall be taken by exploring the commercial option first and then modifying an existing subsystem shall be considered. Emphasis on flexibility shall take precedence over optimality.
  These activities are defined as Systems design for new systems, and Systems Analysis or Value Engineering for existing systems.
  The total system shall be the top-level Configuration item sometimes referred to as first-article when being delivered. The decomposition of the system into lower level subsystems, HWCIs, CSCIs and associated equipment shall be performed using a predetermined policy influenced by ILS and Industry. In general, an item identified as a configuration item shall be considered if its complexity warrants definition with a MRI. An item that warrants a functional specification should also be considered for selection.
  The system and subsystem design shall be documented in a System/subsystem design document.
  Summary
  Systems and subsystems comprise of a hierarchy of products which are comprised of one or more system elements - CSCIs, HWCIs, people, material, data, service, technique, and/or facility.
  As the system engineering process is applied (design by allocation) to define successive lower levels of the product hierarchy, the system elements are eventually identified and defined.
  Each product will be characterterized by its specification, drawings, Source code, etc. Configuration control shall be applied to all configuration items and all products recorded and updated when necessary.
  
• 4.2.4 Interface design and management.
• Systems and subsystems should be defined in logical organizational lines. Interfaces shall be designed between the system and subsystems and the external environment.
  Subsystems should be defined to minimize the amount of information to be exchanged between subsystems.
  Well designed subsystems will only send completed items to other subsystems. Interface requirements shall be documented in an 'Interface Requirements Specification'.
  
• 4.2.5 Functional decomposition.
• Functional decomposition shall:
  • map capabilities to CSCI, HWCI and manual operations;
  • map capabilities to system requirements;
  • ensure that all tasks identified by a statement of work (SOW) are being completed.
• This list shall provide the foundation of the Work Breakdown Structure (WBS) by identifying the activities and the preparation of the Engineering Program Plan.
  In recent years, object-oriented methods of analysis have been used as an alternative to the traditional functional decomposition.

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