Life Cycle Stages
Lead Authors: Mike Yokell Contributing Authors: David Endler, Garry Roedler
A life cycle is the evolution of a system, product, service, project or other human-made entity from conception through retirement. (ISO/IEC/IEEE 24748-1) A stage is a period within the life cycle of an entity that relates to the state of its description or realization. Stages relate to major progress, achievement milestones, or decision points of the entity through its life cycle.
Typical Life Cycle Stages
A system progresses through various life cycle stages that span conception, development, production, utilization, support, and retirement. This naming of stages can be found in (ISO/IEC/IEEE 24748-1), (ISO/IEC/IEEE 15288), and the INCOSE Systems Engineering Handbook (2023). Within each stage, the primary goals are:
- Concept Stage - Identify stakeholders' needs. Explore concepts. Propose viable solutions
- Development Stage - Refine system requirements. Create solution description. Build system. Perform system verification and system validation
- Production Stage - Produce systems. Inspect and test
- Utilization Stage - Operate system to satisfy users' needs
- Support Stage - Provide sustained system capability
- Retirement Stage - Store, archive or dispose of system
Movement between stages represents a milestone or decision point with specific criteria related to stage entry and exit. Life cycle models provide a decision-linked segmentation of the conceptualization, development, production, utilization, support, and retirement of the system. Any system of interest can be regarded from the perspective of one or more life cycle models. Some life cycle models permit iteration and concurrency of stages while some do not. Which stage(s) a system of interest is in depends on the life cycle model. A system of interest can be in multiple life cycle stages at the same time.
Entry and Exit Criteria
Entry or exit criteria can be met (diamonds in Figure 1) before the decision, concurrent with the decision, after the decision, or not at all (triangles). Decision criteria can include an assessment of technical debt and its implications for other stages. The existence of technical debt in the system negatively impacts design suitability. Technical debt can accumulate in any life cycle stage.
A system life cycle model can be segmented by stages to facilitate planning for the system of interest. Decision-making reviews or gates can be used to inform the progression between stages to reduce risk and to enable satisfactory progress. These gates can be based on specific entry or exit criteria leading to informed decisions that can facilitate consistent outcomes as the system transitions between stages. It is important to note that not all parts of an SOI will reach the same maturity and therefore decision gate at the same time. Therefore, interim maturity reviews are essential to keep timely awareness. Also, it is necessary to be clear about tailoring the entry/exit criteria - one size does not fit all.
At a decision gate, the actual progress is evaluated against criteria expected for each stage or for an increment of the system that can be independent of other increments. Generally, there are two elements to the review: looking backwards at the progress to date and looking forwards to the preparedness to continue. Criteria determine when a stage can be exited and when other appropriate stages can be begun. Technical Reviews and Audits provides additional information. ISO/IEC/IEEE 24748-8 provides more rigorous requirements for technical reviews and audits in support of decision gates for defense projects but can be applied to other types of systems.
In two-party acquisition situations, joint stakeholder reviews between the parties to the agreement can be needed. These joint reviews can support the decision gates between stages.
Decision Options for each stage:
- Begin another stage or stages
- Continue this stage
- Go to or restart another stage
- Pause activity
- Terminate
References
Works Cited
INCOSE. 2023. "Chapter 2.1.2" in Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities, 5th Edition. Ed(s): D. Walden, T.M. Shortell, G.J. Roedler, B.A. Delicado, O. Mornas, Y. Yew-Seng, D. Endler. San Diego, CA: International Council on Systems Engineering (INCOSE). Available at https://www.incose.org/publications/se-handbook-v5.
ISO/IEC/IEEE 15288. 2023. Systems and software engineering — System life cycle processes. Geneva, Switzerland: International Organization for Standardization (ISO), International Electrotechnical Commission, and Institute of Electrical and Electronics Engineers. Available at https://www.iso.org/standard/81702.html.
ISO/IEC/IEEE 24748-1. 2024. Systems and software engineering — Life cycle management, Part 1: Guidelines for life cycle management. Geneva, Switzerland: International Organization for Standardization (ISO), International Electrotechnical Commission, and Institute of Electrical and Electronics Engineers. Available at https://www.iso.org/standard/84709.html.
Primary References
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Additional References
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