System Affordability

Affordability is the balance of system performance, cost, and schedule constraints over the system life while satisfying mission needs in concert with strategic investment and organizational needs (INCOSE 2010). Design for affordability is the practice of considering affordability as a design characteristic or constraint. This topic continues the theme of part 6 by discussing this important 'ility.'

Overview

Increasing competitive pressures and the scarcity of resources create a high priority for systems engineering (SE) techniques to improve systems affordability. Several recent initiatives have made affordability their top, technical priority and recommend improved systems autonomy and human performance augmentation as research priorities to reduce labor costs, provide more efficient equipment to reduce supply costs, and to create adaptable systems that cost-effectively extend the usefulness of a system’s lifetime.

Yet, methods for cost and schedule estimation, and more affordable systems development processes, have not changed significantly to address these new challenges and opportunities. New methods are needed for better cost and schedule estimation, such as tradeoff analyses between cost, schedule, effectiveness, and resilience; and methods to adjust priorities and deliverables to meet budgets and schedules, all in the context of the rapid changes underway in technology, competition, operational concepts, and workforce characteristics.

Background

In many cases, cost and schedule estimation is decoupled from technical SE tradeoff analyses and decision reviews. Most models and tools focus on evaluating either cost-schedule performance or technical performance, but not the tradeoffs between the two. The INCOSE SE Handbook now includes affordability as one of the criteria for evaluating requirements (INCOSE 2010), and a working group was chartered to advance the state of the practice for Design for Affordability (INCOSE AFFWG 2010).

However, organizations and their systems engineers have often focused on affordability to minimize acquisition costs. They are drawn into the easiest first approaches that would produce early successes, but frequently also produce brittle, expensive-to-change architectures that increase technical debt and life cycle costs. This has created a stronger focus on SE focused on maintainability, flexibility, and evolution (Blanchard-Verma-Peterson 1995).

Affordability is related to other topics involving cost and schedule. System Analysis considers cost and affordability in the technical design space. Planning is the management activity where cost and schedule estimates are developed and used in project execution.

Modularization

A key SE principle in this regard involves modularization of the system’s architecture around its most frequent sources of change (Parnas 1979). Then, when changes are needed, their side effects are contained in a single systems element, rather than rippling across the entire system. This approach creates needs for three further improvements. One method of improvement is to refocus the system requirements, on not only a snapshot of current needs, but also on including the most likely sources of requirements change or evolution requirements. Another method is to monitor and acquire knowledge of the most frequent sources of change to better identify requirements for evolution. A third method is to evaluate the system’s proposed architecture to access how well it will support the evolution requirements, as well as the initial snapshot requirements.

An extension of this approach is to identify families of products or product lines in which the systems engineers identify the commonalities and variability across the product line, and to develop architectures for creating (and evolving) the common elements only once with plug-compatible interfaces for inserting the variable elements (Boehm-Lane-Madachy 2010). This approach has been extended into principles for service-oriented system elements, which are characterized by their inputs, outputs, and assumptions, and which can easily be composed into systems in which the sources of change were not anticipated.

This approach can also be extended into classes of smart or autonomous systems, which include many sensors that identify needed changes, and autonomous agents that can determine and effect such changes in microseconds, or much more rapidly than humans can. Such autonomy can not only reduce reaction time, but also reduces the amount of human labor needed to operate the systems, thus improving affordability.

Pitfalls

There are pitfalls for the unwary. There are several hazardous failure modes for autonomous systems. For example, one failure mode is system instability due to positive feedback. An agent will sense a parameter reaching a control limit and give the system a strong push in the other direction, after which the system will rapidly approach the other control limit, causing the agent (or another) to give it an even stronger push in the original direction, and so on. Another is that autonomous agents are frequently self-modifying, which makes their failures difficult to debug when the failures occur after several self-modifications. Another is the well-known weakness of autonomous agents to perform commonsense reasoning regarding why human operators have made system control decisions, and to make the wrong conclusions and resulting decisions about controlling the system. Another potential problem is that multiple agents may make contradictory decisions about controlling the system and lack the ability to understand the contradiction or to negotiate a solution that will resolve it.

Practical Considerations

Practical considerations highlight the need for human supervision of such autonomous systems along with better methods for trend analysis and human visualization of undesired trends. It also implies extending the focus from life cycle costs to total ownership costs, which include the cost of owning systems whose failures include losses in sales, profits, mission effectiveness, or human quality of life.

This creates a further need to evaluate affordability with respect to the value added by the system under consideration. In principle, this involves evaluating the system’s total cost of ownership with respect to its mission effectiveness and resilience across a number of operational scenarios. However, determining the appropriate scenarios and their relative importance is not easy, particularly for multi-mission systems of systems. Often, the best that can be done in this regard involves a mix of scenario evaluation and evaluation of general attributes, such as cost, schedule, performance, etc.

Further, this brings to light the challenge that different success-critical stakeholders will have different preferences, or utility functions, for these various system attributes, and that converging on a mutually satisfactory choice among the candidate system solutions involves the resolution of the multi-criteria decision analysis (MCDA) problem among the stakeholders (Boehm-Jain 2006). This is a well-known problem with several paradoxes, such as Arrow’s impossibility theorem that describes the inability to guarantee a mutually optimal solution among several stakeholders, and several paradoxes in stakeholder preference aggregation in which different voting procedures will produce different winning solutions. Still, groups of stakeholders need to make decisions, and various negotiation support systems enable people to better understand each other’s utility functions and to arrive at mutually satisfactory decisions in which no one gets everything that they want, but everyone is at least as well off as they are with the current system.

Works Cited

INCOSE, Systems Engineering Handbook, INCOSE-TP-2003-02-03.2, January 2010, p. 79.

INCOSE AFFWG, INCOSE Affordability Working Group (AFFWG) Charter, http://www.incose.org/about/organization/pdf/AFFWG_Charter.pdf, 2010

Blanchard, B., D. Verma, and E. Peterson, Maintainability: A Key to Effective Serviceability and Maintenance Management, Wiley, 1995.

Parnas, D. L. Designing software for ease of extension and contraction, IEEE Trans. Software Engineering SE-5(2), 128-138, 1979.

Boehm, B., Lane, J., and Madachy, R. Valuing System Flexibility via Total Ownership Cost Analysis, Proceedings, NDIA SE Conference 2010, October 2010.

Boehm, B. and Jain, A., "A Value-Based Theory of Systems Engineering," Proceedings, INCOSE 2006.

Primary References