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The Six Principles of Systems Engineering

IBM's Rational Rules Developed Over 10-Year Period

IBM Rational's six principles of systems engineering are a set of high-level systems development guidelines derived from the careful analysis of successful, complex systems development engagements over the past ten years.

Although they are neither comprehensive nor mutually exclusive, they serve to highlight key areas of focus for organizations interested in quickly building expertise in complex systems development. They also serve as a "measuring stick" for assessing potential problem areas and the root causes underlying symptomatic project deficiencies or failures. It is well-known and accepted that function, schedule, and cost are three key and mutually dependent aspects of project management -- make a change to one, and the effects often ripple through the other two.

A similar relationship exists in product and program management for complex systems development. As shown in Figure 1, the three key aspects are:

  1. Systems architecture
  2. Organizational structure, including the systems development infrastructure
  3. Process, including workflows, best practices, and the like
These aspects collaborate to help achieve the following:

  • "Build the right system and build the system right"

    Architecture focuses on building the right system and model-driven use-case based architectural decomposition lays the foundation for building the system right. Why is architecture singled out? Because it provides the foundation on which the system is ultimately constructed. The choices made in selecting the system's architecture become a lasting legacy - either good or bad.

    Here's a transportation example: The basic architecture used for centuries in building roads or other transportation elements (like rail tracks) was basically point-to-point (the shortest distance between two points can be considered optimal since it minimizes the road length and one would assume maximizes time to travel efficiency). Simple enough, but there was always at least a physical constraint: the terrain, which forced the path to avoid obstacles. There were also other potential constraints such as "hostile" territory or political boundaries.

    In any case, roads were built and paths crossed somewhat haphazardly. Move forward to the 20th century. Population growth generated additional constraints - namely street lights or traffic signs to optimize the flow of traffic through intersections. These are somewhat problematic on roads architected in the point-to-point avoid obstacle approach, especially where more than two roads intersect. A clearly "better" architecture has proven to be laying out roads in rectangular grids. This architecture and the many implementations are much easier to control from a signaling and traffic flow perspective.

    So build the right system and build it right - making it robust (scalable, extendible, easy to maintain, easy to use, and so on).

  • "Do the right things, and do the things right"

    The systems development framework focuses on defining the right things to do throughout the product lifecycle to optimize business value and return on investment and best practices, processes/supporting tools and governance (requirements, quality, change, configuration, and program/project management) focus on ensuring things are done right.

  • "Apply the right resources, and apply the resources right"

    "Doing" and "building" are action verbs; they require resources to perform the "doing" and the "building". The most significant enterprise resource is people, followed by supporting infrastructure. Acquiring, motivating, and retaining skilled personnel applies the right resources, and aligning the organization appropriately to optimize communication, collaboration, and effort applies the resources optimally. A sound enterprise infrastructure (including IT equipment and software) is one key aspect in ensuring the resources are applied optimally, once again maximizing business value and return on investment

    The six principles of systems engineering address all three aspects described above. The three technical principles (noted below) focus on architecture and the derivation of system models, while the remaining principles provide the complementary infrastructures and workflows needed to optimize the technical development environment.

    The six systems engineering development principles are:

    1. Decompose systems, not requirements (technical).
    2. Enable both separation and integration of "key systems development" concerns (technical).
    3. Specifications flow up and down the architecture (technical).
    4. Systems and components collaborate; so should development teams.
    5. Development organizations should reflect product architectures.
    6. Base the "development" lifecycle on removing risk and adding value.
    Let's examine each of these principles, initially from a generic systems engineering view, and then specifically in the context of joint hardware/software development.

    Decompose systems, not requirements
    Since systems and software engineering principles and methods have been written about, discussed, and applied in countless cases, one might think that development teams have a common understanding of such terms as "system" and "systems engineering." Unfortunately, this is not the case; neither across enterprises within a specific industry nor across the product and functional domains within an engineering development community in a single enterprise.

    According to INCOSE (the International Council on Systems Engineering), systems engineering is2:
    An interdisciplinary approach and means to enable the realization of successful systems. It focuses on defining customer needs and required functionality early in the development cycle, documenting requirements, and then proceeding with design synthesis and system validation while considering the complete problem:

    • Operations
    • Performance
    • Test
    • Manufacturing
    • Cost and Schedule
    • Training and Support
    • Disposal
    A system is a group of interacting, interrelated, or interdependent elements forming a complex whole, which provides a set of services that are used by an enterprise to carry out a business purpose (mission). System components consist of hardware, software, data, and workers3. Put simply, a system is a complex entity that provides some tangible result of value. Systems engineering is a disciplined approach that helps us examine desired results and determine what can satisfy them. It also helps us determine how to do this within a set of business-critical constraints (cost, schedule, testing parameters, ease of manufacturing, and so on). The "what" is the system, the "how" is the functional requirements, the "business-critical constraints" are the supplementary requirements, and the "desired results" are products of use cases.
  • More Stories By Murray Cantor

    Murray Cantor is a member of the IBM Rational CTO team, taking the lead for Governance and Systems. Cantor formerly lead the IBM Rational field services group, promoting and extending Rational best practices, and working closely with customers on innovative ways to build and deliver systems more efficiently.

    More Stories By Gene Roose

    Gene Roose is a senior systems engineering consultant for IBM Rational, concentrating on model-driven systems development methods. He assists clients with solution analysis and design, architectural derivation and validation, and overall project management.

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