[ASEP-Prep] #1. What is System LIFE CYCLE?

The ASEP-Prep series is a brief summary of the contents of Systems Engineering Handbook 5th, which I studied while preparing for the INCOSE Knowledge Exam, and only the contents that I think are relevant to the scope of the exam.

Because the content of SE Handbook is somewhat abstract and broad, it is easy to get lost while reading the book. However, I think that if you learn the general content of the book and then study the details, you will be able to achieve more readability and be less stressed while reading the SE Handbook.

And after actually taking the test, I will post about the insights and information I personally felt and the scope of the test in the last post of this series.

What is System LIFE CYCLE?

The primary goal of systems engineering (SE) is to successfully realize systems that achieve optimization among competing stakeholder goals. To achieve this, the entire work is divided into stages, and at the end of each stage, the satisfaction and risk level of the system characteristics are reviewed. The steps do not necessarily have to proceed sequentially and can be executed multiple times or in parallel as needed. What is important in this process is the concept of specific decision points, so-called ‘decision gates’, that determine the progress of each step. These stages, which can be compared to the growth stages of a living organism, are called the system life cycle.

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Looking specifically at the characteristics of the system life cycle, the system’s goals are achieved through several stages. (See Figure 1) Each step can be entered as many times as necessary, and may overlap or occur simultaneously rather than sequentially. During the exit phase, only specific elements may be retired rather than the entire system.

Each stage has entry and exit decision gates, which help ensure that the objectives of that stage have been achieved and that the risks of moving forward are acceptable. Additionally, key elements of the system have their own life cycles, which must be managed over time as an integrated System of Interest (SoI). Decision gates must be coordinated with each other to ensure efficient integration of system elements. These structures are linked to various system life cycle models to support gradual integration into the final SoI.

Life Cycle Statges

The life cycle of a system progresses through the stages of conceptualization, development, production, utilization, support, and retirement. Each stage has its own characteristics, and in different life cycle models the names and characteristics of the stages may be different. Each stage must be managed adaptively according to the requirements of the system, and may require appropriate adjustments according to different life cycle models. This plays an important role in ensuring that the system evolves efficiently and successfully achieves its goals at each stage.

1. Concept Stage: The concept stage begins with recognizing the need for a new mission or business capability, and solutions are explored through several methods. At this stage, the problem and solution space are clearly defined, and business or mission requirements, stakeholder needs and requirements are identified.

It also predicts cost, schedule, and performance. Risk assessment and management are important, and stakeholder feedback is important. Outputs from the concept phase include operational concepts, support concepts, and initial architectural solutions. Decisions at this stage shape the possibilities for change in subsequent stages, and it is important to note that incremental changes may limit future possibilities.

2. Development Stage: The development stage defines a system that satisfies the essential characteristics of the system and the requirements of stakeholders while considering production, utilization, support, and retirement. During this process, we balance the system and optimize key parameters through system analysis, trade-off analysis, modeling, simulation, and prototyping.

A key part of the development phase is establishing an engineering baseline to ensure that the system can be produced, utilized, and supported effectively over the long term and prepared for responsible retirement when necessary. The goal at this stage is to meet stakeholder expectations and includes system requirements, architecture, design, documentation, and various plans. Key deliverables include prototypes, supporting system requirements, integration and validation plans, risk management, and staffing and training plans.

3. Production Stage: The production stage begins with approval to implement the baseline of the development stage into an actual system. In complex systems, approval may only occur for some system elements. At this stage, the system is realized and certified for use, ready for installation and transition to further stages. Key deliverables include realized system parts and documentation to be used during utilization, support, and retirement phases. These documents are important sources, providing all the information needed to implement and manage the system.

4. Utilization Stage: The utilization stage begins with the transition to use of the system or its parts. At this stage, support systems are utilized to enable the system to function in its intended environment. The utilization phase is longer than the other phases, and modifications to the product occur frequently to address deficiencies in the system, improve functionality, or extend its life.

In this phase, documentation from previous phases is maintained, and technical management processes such as configuration management and risk management are strengthened and applied on an ongoing basis. Finally, the utilization phase runs parallel to the support phase and concludes with the phase-out of various parts of the system.

5. Support Stage: The support stage begins with support preparation for system utilization, and support planning and acquisition are carried out before utilization. At this stage, defects and failures are identified and used as a basis for problem solving or evolutionary changes to the system. Proposed modifications are needed to reduce operating costs, improve supportability, and extend system life, which requires engineering evaluation to prevent loss of system functionality. The support phase ends when it is determined that the system is no longer useful or requires support.

6. Retirement Stage: At the retirement stage, the system is removed from operation, and SE activities at this stage are focused on ensuring that disposal requirements are met. Retention of documentation generated during the utilization and support phases can be important. Decommissioning planning must be included as part of the system definition during the concept and development stages, as decommissioning without an initial plan can have negative consequences.

Decision Gates

Decision gates are risk management decision points located at the beginning and end of each stage, and serve to clearly manage the progress of the project. These gates are often in the form of project milestones and reviews, verifying the readiness and achievement of the phase’s goals. The purpose of the decision gate is to ensure that the system has increased maturity, that the project deliverables meet the business case, that sufficient resources are available, that any outstanding issues are resolved, and that overall risk is accepted. Each gate allows you to choose to proceed to the next step, continue the step, restart the previous step, put the project on hold, or end it.

In some approaches, such as agile, the frequency and format of decision gates vary, with more frequent and informal interactions. Approval of the decision gate is based on expert and stakeholder review and must confirm compliance with appropriate standards. Incorrect reviews or omission of decision gates can lead to long-term cost overruns and delays.

Upon successful decision gate completion, deliverables such as documentation, analysis results, and models are accepted and used as the basis for future work. These deliverables are managed through configuration management, along with the rationale and assumptions associated with the decisions. Balancing the formality and frequency of decision gates is considered a critical factor in the success of any systems engineering process.

Technical Reviews and Audits

Technical reviews and audits play an important role in assessing the technical progress of a system, coordinating activities, and verifying the technical health of the system during its life cycle. A technical review is a systems engineering activity that evaluates the progress of a project against technical requirements, while an audit is a detailed review that verifies compliance with product definition information and requirements. These activities are specified in the project’s Systems Engineering Management Plan (SEMP) and may be part of a decision gate review.

Technical reviews and audits assess whether the SoI meets requirements and stakeholder expectations, has acceptable quality characteristics, and has appropriate maturity and risk levels. During this process, the verification and validation path for the SoI must be clear.

Effective technical reviews and audits require establishing a review plan, eliminating unnecessary reviews, establishing clear entry and exit criteria for each review, adopting a risk or event-driven approach, and involving subject matter experts and independent reviewers. Additionally, all members of the team must be involved and clear actions and ownership must be established for any issues that arise. This allows you to effectively manage the technical requirements of your system and ensure the successful progress of your project.

Lifecycle Models

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A life cycle model defines how each phase of a project is planned and executed. Sequential, incremental, and evolutionary are the three main life cycle model approaches widely used in systems development. Each model can be selected depending on the characteristics and needs of the project.

1. Sequential Lifecycle Model

  • Sequential model, sometimes also known as waterfall model, is a linear approach in which each development stage begins only after the previous stage has been fully completed.
  • This model is effective when each step is clear and structured and requirements are well defined and unchanging.
  • The disadvantage is that all requirements need to be fully understood and defined at an early stage, which can be expensive and time consuming if changes are required at a later stage.

2. Incremental Lifecycle Model

  • The incremental model divides the entire system into several small parts and develops each part in turn.
  • Each “increment” is a working part of the system that goes through several stages until it is fully developed and integrated.
  • This approach is useful when you want to build a large project incrementally by breaking it into smaller units that are more manageable and reduce risk.
  • Some features of the system will be made available initially, and additional features will be developed and integrated in subsequent increments.

3. Evolutionary Lifecycle Model

  • Evolutionary models use prototypes to iteratively develop and improve systems.
  • Starting from an early prototype, it develops into a final system through iterative development and feedback.
  • This model is advantageous when requirements are uncertain or highly variable, and user feedback can be quickly incorporated to continuously improve the product.
  • Provides flexibility to quickly respond to market changes or technological developments.

Each model has pros and cons depending on the specific needs and circumstances of the project, and project managers and teams must choose the most appropriate model to ensure project success.

[ASEP-Prep] #2. Agreement and Enabling Processes

[ASEP-Prep] #3. Technical Management Processes

[ASEP-Prep] #4. Technical Processes – Concept and System Definition

[ASEP-Prep] #5. Technical Processes – System Realization, Deploy and Use

[ASEP-Prep] #6. Quality Characteristics



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