A Work Breakdown Structure (WBS) is a methodical way of decomposing the project work into meaningful and logical smaller pieces for the purpose of planning and control. When completed the WBS should include all activities associated with the project scope.
It becomes the data dictionary for communicating on the project. Work Breakdown Structures have a child / parent relationship which means that it's possible to roll up and summarize any information from the lower levels and upwards. This is true for activity cost, resource effort and schedule information.
It can also be used to assign responsibility for groups of activities to different functional managers for planning and or accountability purposes.
It should also be used as the format for capturing and outlining changes to the project. One way of representing the WBS is to outline the format similar to a “Table of Contents” in a book.
An example could be:
Another way is to outline the format like a tree structure similar to a Company’s Organizational Chart.
In any case, the lowest level is known as a work package, which would be made up of a number of activities or tasks with clear resource assignments and functional responsibility assigned.
There is no limits to the level of detail one can go down to, nor there's a need to have the same number of levels for each branch.
However there should be guidelines to assure the desired level:
• assign responsibility of definition and completion for accountability purposes.
• estimate the required resources and their required hours/days of performance.
• estimate the duration (elapsed time) between start and finish of the element.
• identify logical predecessor and successors to the element.
• short enough so that it's possible to define its doneness criteria for control and progress capturing purposes.
Note: The more detail one creates the more time and effort is required to maintain the WBS. One has to decide on the trade off between more control (i.e. detail) and overhead (i.e. amount of data to update).
There are many approaches to breaking down the work into smaller packages. Since the data can be rolled up and summarized into different levels, the approach one initially takes will decide on what kind of information it will be able to report on. Based on one's reporting requirements and type of project, it's possible to mix and match formats at different levels.