What is a work breakdown structure (WBS)?

Work breakdown structure is generally divided into three distinct types: deliverable-based WBS, phase-based WBS and responsibility-based WBS.

This approach identifies the connections between the project’s scope and its deliverables. It decomposes the scope into smaller, more manageable deliverables—usually something specific that must be produced, supplied, or obtained by executing project tasks to satisfy project requirements.

The phase-based WBS breaks the project down into five distinct stages: initiation, planning, execution, control and close. Within each of these stages are unique deliverables.

A responsibility-based breakdown defines the structure of the project based on the teams, individuals and organisation units that will be working on the project. While the second level of the structure will identify who is responsible to complete the tasks, the subsequent levels follow a similar format to other WBS types, identifying deliverables that must be completed to move the overall project forward.

Additionally, there are several less-common approaches to WBS. These include the following:

• Verb-oriented
  Uses actions to define deliverables.
• Noun-oriented
  Uses components to define deliverables.
• Time-phased
  Breaks projects into separate time-periods or phases.
  

As previously stated, the WBS takes the form of a diagram with the final deliverable at the top and all sub items arranged below it. These sub items are usually divided into four distinct levels or tiers. This allows teams to more easily visualise the steps needed to complete the project. The four levels of a work breakdown structure are top level, controls account, work packages and activities.

At the top of the diagram sits the final deliverable. The top level can also be the project title.

The second level consists of the different main project phases. These are the secondary deliverables that must be completed to ensure a successful project.

The work packages sit under the controls-account level, identifying the necessary tasks that go into the secondary deliverables.

This principal also addresses risk and uncertainty using milestones. The whole The final level consists of the activities that facilitate the work packages.

Essentially, every level is supported by the level that follows it. In a traditional breakdown diagram, this results in a branching chart that flows downwards from the final deliverable, taking into account all of the essential tasks, activities and deliverables that need to be performed to complete the project.

Although the aforementioned approach may be the most widely used of WBS diagrams, it is not the only option. There are several different variations of the classic WBS diagram, including the following:

As described above, the tree-diagram WBS represents the workflow as branching elements leading down from the primary project deliverable. Each level is made up of tasks that support the level above it. This is the most-common approach to WBS diagramming.

Although not as detailed as some other options, the WBS list may be the simplest and easiest option for organisations who just need a quick outline of deliverables and subtasks. It consists of little more than a list identifying and breaking down important tasks.

All of the information presented in the tree diagram can be just as easily represented and organised using a spreadsheet. The spreadsheet approach uses columns and rows to detail the various levels, tasks and deliverables. Spreadsheets are often dynamic, shared documents that can be updated in real time to account for any changes to the project.

Using project management software, organisations can create detailed Gantt charts capable of linking relevant information, applying discrepancies, setting milestones and more. These charts are similar to spreadsheets in that they allow for dynamic updating, but they also function as a timeline for the project itself.