Decomposition

November 3, 2009
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Decomposition is the activity of breaking down project deliverables iteratively. This is continued until the lowest level is reached, this level is the work package level. Work packages are set of activities that are so well defined that cost estimates and time estimates of these sets of activities can be done reliably and accurately. The level of details described in the work packages, obviously depends on the type and complexity of the project.

Decomposition method

Decomposition is an iterative method. At the top level of the WBS structure, which is essentially a tree, are the deliverable objectives indicated as branches from the project level. The deliverables may be indicated as phases of the project, specific deliverables, a set of subprojects or a mix of these. Deliverables and related work are identified and analyzed to create the next level of the WBS. As this activity is continued each branch of the WBS keeps generating multiple branches at the lower level. This continues until you reach the work package level. The organization/ reporting relationship like diagramming is maintained. Each component is identified. One such representative diagram is illustrated in the PMBOK at diagram 5.8. The element numbering can simply represent the level and the branches generated from that level. For example, when level 2 branches off to three activities they can be numbered 2.1, 2.1 and 2.3 etc. the lowermost nodes are identified as the work packages and the same numbering is continued right through. At every step you must verify and confirm that further decomposition is necessary and sufficient. This stops at the work package level which are, as mentioned earlier, a set of activities that can be estimated (time, cost) for the purposes of planning the project.

There are several ways one can go about creating the work breakdown structure. You may start with the project lifecycle phases at the first level of decomposition. Product and project deliverables then can be added at the next level. Fig 5-9 is an illustrative figure of this kind of decomposition.

The first level of decomposition could be the major deliverables, Fig 5-10 of PMBOK is an illustration of this mode of decomposition. Decomposition can also be based on sub projects that are contracted out to agencies other than the project team. The contractors then are responsible for developing the WBS for the parcel of work assigned to them.

It is possible to get carried away and decompose to too much detail. While details help plan, manage and control the work; too much detail can be counter productive. The time and effort of management personnel will increase to co-ordinate too much of detailed activities. It will lead to inefficient use of resources and decreased efficiency in performing the work. So the trade off really is simplifying things but no further (as Einstein is reputed have said).

The details to be achieved are the level at which one has a clear definition of the work package and the estimates can be made accurately. The decomposition proceeds by breaking down the deliverables into its fundamental components. These components should represent verifiable products, services or results. What kind of diagramming is used is not mandated. It could be like an organization structure, as indicated in the illustrations discussed here. The structure could be depicted as a fishbone diagram too. In fact, it could be any diagram that shows up the structural relationships clearly.

A quick test of verification of decomposition process is to confirm that the lower level components are necessary and sufficient to generate the higher level element. This test needs to be applied at every level as the structure grows. The structure is not likely to reach the same levels of decompositions for all the deliverables. Some deliverables that are simpler, could decompose into a work package in one or two levels of decomposition while there may be other activities that would have to be refined for many more levels.

Sometimes it is not possible to decompose activities which may be required some time in future. The decomposition is undertaken only when this part of the work, specific deliverable or sub project are clearly understood. This, thus can be a continuing activity and are often called a rolling wave planning.

There is a so called 100% rule that must be applied to the WBS structures. The structure must take care of 100% of the work and nothing more. For that, lower level elements must roll up to higher level activities. Iteratively the complete set of work packages must thus roll up to the complete projects and no other extra work. When we say work, that includes work not only to produce the deliverables but the project management work, documentation work and everything else that are necessary activities. The “Practice Standard for Work Breakdown Structures” from PMI has detailed methods of creating such structures including industry specific templates that could be used.

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