Characteristics of project life cycles

A project life cycle is a collection of generally sequential phases. The common characteristics, as described in PMBOK, are as follows.

Characteristics

1. Phases are sequential and sometimes overlap: each phase ends with the transfer of a deliverable, such as a design document or prototype.
2. Cost and staffing levels are low at the start, peak in the middle (execution), and drop rapidly near the close.
3. Risk and uncertainty are highest at the start. As the project proceeds the probability of successful completion normally improves.
4. Stakeholders' influence is highest at the start and gradually decreases as the project progresses.
5. The cost of changes and of correcting errors increases as the project continues. A requirement error found in testing costs far more than one found in analysis.
6. Each phase has defined deliverables and entry/exit criteria.
7. Phase-end reviews (gates, kill points) decide whether to continue, modify or stop the project.
8. Different skills and resources are needed in different phases.
9. Phases are time-bound and are usually named after the main work, e.g. design, build, test.
10. Life cycles may be predictive, iterative, incremental or adaptive, according to how well the requirements are known.

Cost of change
  |                      /
  |                  ___/
  |             ____/
  |____________/
  +----------------------> time
  Concept    Execute    Close

Illustration

In an ICT project, most staff are engaged during coding and testing (peak effort), while few are needed during concept and close-out. Feasibility reviews at the end of concept stop weak projects before major spending.

These characteristics guide the manager on when to invest in planning and risk reduction: early on, when influence is highest and change is cheapest.