What is Decomposition?
Decomposition is the technique of breaking scope into smaller, more manageable pieces — the engine behind the WBS (deliverables into work packages) and activity definition (work packages into activities). Stop when pieces can be reliably estimated and assigned; going further adds bookkeeping, not control.
The judgment call is granularity: the 8/80 heuristic (packages between 8 and 80 hours) is a guide, not a law — decompose near-term work finely and future work coarsely (rolling wave).
Worked example
"Install substation" decomposes: civil works → foundations, cable trenches, fencing; electrical → transformer setting, busbar erection, protection panels; each to packages a single crew can own and a scheduler can estimate from norms. The team stops decomposing "fencing" at one package — splitting it into posts, wire, and gates would manage nothing anyone was worried about.