The Mechanics. Decomposition involves dividing each project deliverable into smaller and smaller pieces until there is enough detail to support scheduling, estimating, and control. Decomposition normally involves the following steps:

1. Add project management to the list of the project deliverables from the project definition document. Treat project management as a deliverable.
2. For each item at the current lowest level, consider whether a reasonable range estimate can be made at this level of detail? Note that the meaning of reasonable is driven by the nature, size, and timing of the deliverable. A small, well-defined item that is due next week needs a relatively small range estimate to be deemed reasonable. An item whose requirements are not yet defined may have a very large range of possible outcomes and still be reasonable. If you decide that you can develop a reasonable estimate at this level of detail, go on to the next item; if not, proceed to step 3.
3. Create additional detail by identifying logical sub-elements of the item. For example, the logical sub-elements of a document may be a list of the chapters, or it might be "write, review, revise." Return to step 2.

Fine-tuning. The initial decomposition results must often be revisited during the performance of other planning processes. In addition to the obvious case of product or project scope changes, following is a list of common adjustments:

• During decomposition, the emphasis is on defining and understanding the nature of the work to be done. As a result, the planning team may initially be less than rigorous in its descriptions of the deliverables and later editing may be required.
• Staffing and scheduling decisions may require either more or less detail in some areas of the WBS.
• Changing a "make" decision into a "buy" changes the work to be done.
• Risk response actions may have to be added.

The Results. Properly done, a WBS has the following characteristics:

• One branch is reserved for project management activities and related deliverables such as status reports. All other branches identify major project deliverables from the project definition document.
• All levels except the lowest are described in terms of deliverables (a verifiable, tangible product or result). The lowest level of the WBS is described in terms of activities which must be performed in order to produce the deliverable at the next level up.
• The number of levels may vary by deliverable. Similar deliverables will often use the same or very similar names for sub-deliverables.
• If the project scope includes multiple phases, the phases will normally be included in the WBS, usually at one of the top two levels.