Process Description
A life cycle model provides a framework of processes and activities guiding a system’s life cycle. ISO/IEC/IEEE 24774 standardizes process descriptions to ensure clarity, consistency, and comparability. Each process includes a name, purpose, and outcomes, with optional activities, tasks, inputs, and outputs. Consistent descriptions enhance understanding, compliance, and improvement, supporting systematic, transparent, and adaptable system engineering practices.
Fundamental Concepts
Article Life Cycle Models describes that a life cycle model is a framework of processes and activities concerned with the life cycle. Processes and activities that are integrated into the framework of a life cycle model are often referred to as life cycle processes.
The purpose of ISO/IEC/IEEE 24774, Specification for process description, (available for free at: https://www.iso.org/standard/78981.html) is to “encourage uniformity in the description of processes”. This international standard specifies the way process descriptions should be established and builds on the lessons learned from other international, national, and industry standards that describe processes and process models.
Defining processes in a consistent manner ensures that they are understandable, comparable, and manageable. Consistency provides a common language for describing how work is done, which reduces ambiguity and simplifies collaboration. It enables alignment with standards, regulations, and good practices, ensuring that processes are not only efficient but also compliant. When processes follow a consistent structure, it becomes easier to document, analyze, and improve them systematically. This also supports training and knowledge transfer, as users can quickly grasp and apply established methods.
Processes can be specified using the following elements (ISO/IEC/IEEE 24774):
| Required Element | Optional Elements | For Any Other Element | |
|---|---|---|---|
| Process | Name | Inputs | Notes |
| Purpose | Activities | Controls | |
| Outcomes | Tasks | Constraints | |
| Outputs |
According to ISO/IEC/IEEE 24774, at a minimum, process descriptions include the elements Name, Purpose, and Outcomes. Additional details, such as inputs, outputs, activities, or tasks, can be added if needed but are not mandatory. The core elements capture the goals and objectives of the process, focusing on the intended results without requiring a detailed structural breakdown. By defining processes in terms of Name, Purpose, and Outcomes, organizations establish a clear and consistent foundation. This approach ensures that processes can be easily understood, implemented, and assessed, while still allowing for further elaboration if deeper analysis or refinement becomes necessary.
Elements of Process Description
Process Name (Required)
The name of a process should be a concise noun phrase that clearly identifies its main focus and distinguishes it from other processes. Verbs should be avoided because they can lead to situations where the process name resembles activities or purposes.
Process Purpose (Required)
The purpose of a process should express one or more high-level goals that define why the process is performed. It helps clarify the scope and boundaries, especially when processes appear to overlap. Ideally, the purpose is stated in a single, concise sentence, beginning with “The purpose of the xxx process is...”. It should not summarize activities or outcomes, and the use of “and” should be avoided to prevent listing unrelated goals. Additional context or explanations can be provided separately in notes or supporting text.
Process Outcomes (Required)
Process outcomes represent measurable and observable results or change of state achieved by executing a process. Unlike outputs, they are not defined as documents, records, or information items, but rather as tangible technical or business achievements. Each outcome should be written as a single, present-tense declarative sentence, expressing a clear, positive objective such as delivering a service, achieving a change of state, maintaining a desired condition, or meeting defined requirements. To ensure clarity, outcomes should avoid conjunctions like “and” or “and/or”, separate statements should be used instead. Typically, a process should have three to seven concise outcomes, each directly supporting its stated purpose. Outcomes are distinct from benefits, which describe broader organizational gains and can be recorded separately as informative notes.
Process Activities (Optional)
According to ISO/IEC/IEEE 24774, activities are defined as “set of cohesive tasks of a process”. Process activities describe the broad actions undertaken to execute a process. They group related tasks (see below) to improve understanding and communication and can, if cohesive and well-defined, be treated as lower-level processes with their own purposes and outcomes. All activities together must achieve the process outcomes and purpose. Activities should be strongly related internally (across its tasks) but loosely connected to other activities. They are not sequential steps but ongoing responsibilities, avoiding imposed timing or order unless explicitly required.
Process Tasks (Optional)
According to ISO/IEC/IEEE 24774, a task is defined as a “required, recommended, or permissible action, intended to contribute to the achievement of one or more outcomes of a process”.
Process tasks specify concrete requirements, recommendations, or permissible actions that guide the execution of a process. They are written to support the achievement of process outcomes but do not need to fully cover the scope of an activity. Instead, tasks can be seen as discrete points within the broader space of processes and activities. Additional tasks can be included to clarify conformance requirements or to support higher capability levels. Timing or sequencing should not be assumed unless explicitly stated, ensuring flexibility across different life cycle models.
Process Inputs (Optional)
Process inputs are items that get transformed into outputs through the execution of the process, excluding the human or automated resources that perform the work. Inputs can originate from other processes, organizational resources, suppliers, or external sources. While specifying inputs is optional, it becomes essential in closed-loop life cycles.
Process Outputs (Optional)
Process outputs can be specified in descriptions but are optional if outcomes can be demonstrated. Some outputs are essential deliverables, while others serve only for validation or audit. They are generally categorized as artefacts (e.g., prototypes, models, components, or services) or information items with defined characteristics. Artifacts further include four generic work product types: services, software, hardware, and processed materials.
Process Notes (For Any Other Element)
Process notes contain further information on the what, how and why. In many cases, they explain the interrelationship with other processes and also main contain brief examples.
Process Controls and Constraints
Process controls and process constraints guide or restrict how a process is performed, and to some extent when. Controls can originate from laws, regulations, organizational policies, voluntary standards, or agreements with suppliers and customers. Constraints often stem from external environmental or business conditions. They can be documented in a dedicated section of the process description or included as notes alongside other process elements.
Elaboration
In INCOSE SEHv5 section 2.3 a common structure has been applied to describe the system life cycle processes. To maintain alignment with ISO/IEC/IEEE 15288, the purpose statements from the standard are reproduced verbatim for each process described in INCOSE SEHv5. Similarly, the titles of process activities follow the standard, describing what should be done rather than how to perform the tasks. Additional elements are included in some cases to summarize industry best practices and recent developments in systems engineering processes. Process elaborations provide further details specific to each life cycle process.
Each system life cycle process is also represented by an input-process-output (IPO) diagram, showing typical inputs, activities, and typical outputs. While the outcomes are included in ISO/IEC/IEEE 15288, they are not included in INCOSE SEHv5. Instead, INCOSE SEHv5 contains typical inputs and outputs for each process.
They can take any form (e.g., database, document, model, etc), and combinations of inputs and outputs in one artifact are also possible. The names of the inputs and outputs can vary depending on domain, company, or project.
In INCOSE SEHv5, controls and enablers are typically excluded from input-process-output (IPO) diagrams, in figure 1 they are noted, showing how inputs are transformed into outputs under process controls.
These diagrams illustrate one possible way to perform the process, not a mandatory approach. Outputs often represent results captured as documents, artifacts, or models, rather than being produced solely because they are listed.
References
Works Cited
INCOSE. 2023. "Chapter 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. 2023. Systems and software engineering — System life cycle processes. Geneva, Switzerland: International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), and Institute of Electrical and Electronics Engineers (IEEE). ISO/IEC/IEEE 15288:2023.
ISO/IEC/IEEE. 2021. Systems and software engineering — Life cycle management — Specification for process description. Geneva, Switzerland: International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), and Institute of Electrical and Electronics Engineers (IEEE). ISO/IEC/IEEE 24774:2021.
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