Create WBS vs Decomposition for PMP Exam

Create WBS vs Decomposition for PMP Exam

“Create WBS” and “Decomposition” are often used together in the PMBOK® Guide to describe the process of understanding project deliverables for time and scope management. Though they are often used together, these two terms actually carry different meanings and should not be confused.

Create WBS and Decomposition

  • Create WBS (Work Breakdown Structure): Create WBS is a process for Project Scope Management.
    • The primary aim of Create WBS process is to provide a hierarchical / organization chart for better depiction of project scope for activities, costs, quality, risks, etc. identification, estimation and control.
    • WBS (Work Breakdown Structure) is the primary output of the Create WBS process.
    • The WBS Dictionary is also created to supplement the WBS with additional information/attributes for each work packages.
    • The WBS consists of many layers:
      • Deliverables
      • Planning Packages
      • Control Accounts — when all the work packages under a control account have been completed, this will trigger some monitoring and controlling activities to be performed
      • Work Packages — the lowest level component of WBS, by common practice, a work package is the amount of work assigned to a single resource that can produces a verifiable outcome
    • The creation of WBS follows the 100% rule — the WBS must include 100% of the work defined by the project scope and captures all deliverables and there is no overlap between different work packages
    • WBS is NOT a project plan or schedule not it is an exhaustive list of all works to be performed in the project (e.g. project management products/processes are not included).
    • Each WBS component must have a unique code (code of account).
  • Decomposition: Decomposition is the primary tool for the process of Create WBS in Project Scope Management.
    • Decomposition will break down deliverables into small enough components to be considered as a Work Package.
    • The Work Packages are then used for work effort, cost, and time estimation.
    • The Work Packages will need to be further decomposed into Activities and then Tasks later on for more accurate time estimation with activity sequencing.

Note: In the PMBOK® Guide, there is no recommended or fixed way of how detailed the “Work Package” or the “Activity” need to be, and that would depend on the project/organization needs.

Illustrated Example

Let’s again take the project of PMP Exam preparation as an example. The following are my “work packages” to be included in my exam prep (please note WBS and Work Packages would usually be based on the deliverable and intended outcomes):

  • Fulfil the Exam Registration Requirements
  • Revise the Exam Syllabus
  • Assess My Readiness
  • Take the Exam (and pass in first try)

These together will form the ultimate goal of getting PMP Certified. Let’s take the first “work package” as an example. By decomposition, the work package “Fulfil the Exam Registration Requirements” can be further broken down into the following activities:

  1. Get 35 Contact Hours of Project Management Education
  2. Get enough project management experience
  3. Fill in the online exam registration form
  4. Pay the exam fee
  5. Respond to the audit request

Of course, these activities can be further decomposed into smaller activities. But care has to be taken to balance the level of details captured through decomposition. If the WBS and Activity List are overly detailed, valuable time might be required for the unnecessary details and the project will look overly complicated.


Remember this: Creating WBS requires the tool of “Decomposition” and yet “Decomposition” will also break down the lowest level of WBS (i.e. Work Packages) into Activities and Tasks.

Creating the WBS is a process for project scope management while the tool “Decomposition” is used in both project scope and time management.

recommended PMP resourcesAdditional FREE PMP resources: 47+ Commonly Confused Term Pairs with detailed explanations. If you found this article useful, you may wish to reference other Commonly Confused Term articles.

Most Popular PMP Certification Exam Articles

Support website running for FREE, thanks!

If you find this post helpful and if you are thinking of buying from Amazon, please support the running cost of this website at no extra cost to you by searching and buying through the search box below. Thank you very much for your help!

Edward Chung

Edward Chung aspires to become a full-stack web developer and project manager. In the quest to become a more competent professional, Edward studied for and passed the PMP Certification, ITIL v3 Foundation Certification, PMI-ACP Certification and Zend PHP Certification. Edward shares his certification experience and resources here in the hope of helping others who are pursuing these certification exams to achieve exam success.

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *

2 Responses

  1. Anastasia says:

    The 100% Rule (Haugan, 2002, p. 17) is one of the most important principles guiding the development, decomposition, and evaluation of the WBS. This rule states that the WBS includes 100% of the work defined by the project scope and, by doing so, captures all of the deliverables—internal, external, and interim—in terms of work to be completed, !!!including project management!!!. The rule applies at all levels within the hierarchy: the sum of the work at the “child” level must equal 100% of the work represented by the “parent”—and the WBS should not include any work that falls outside the actual scope of the project; that is, it cannot include more than 100% of the work.