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By : RanjithKumar Panjabikesan, PMP, Accounts Manager, TBD
Activity:  2 comments  13362 views  last activity : 06 15 2013 15:02:26 +0000
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Break Down Structures – An Overview

Types of Break Down Structures

  • WBS (Work break Down Structure)
  • OBS (Organizational Break Down Structure)
  • RBS (Resource Break Down Structure
  • PBS (Product Break Down Structure)
  • RBS (Risk Break Down Structure)
  • CBS (Cost Break Down Structure


Work Breakdown Structure (WBS)


A work breakdown structure (WBS) in project management and systems engineering, is a tool used to define and group a project's discrete work elements (or tasks) in a way that helps organize and define the total work scope of the project

A work breakdown structure element may be a product, data, a service, or any combination. A WBS also provides the necessary framework for detailed cost estimating and control along with providing guidance for schedule development and control. Additionally the WBS is a dynamic tool and can be revised and updated as needed by the project manager.


Organization Breakdown Structure (OBS)

Term Definition
Organization (al) Breakdown Structure (OBS) is an intermediate level of the Work Breakdown Structure (WBS) in which organizational relationships are identified and used as the framework for assigning work responsibilities.

The OBS groups together similar project activities or “work packages” and relates them to the organization structure. OBS is then used to define the responsibilities for project management, costing, budgeting and project control.

Work Breakdown Structure (WBS) captures all the elements of a project in an organized fashion. Breaking down large, complex projects into smaller project pieces provides a better framework for organizing and managing the project. WBS can facilitate resource allocation, task assignment, responsibilities, measurement and control of the project. The WBS is utilized at the beginning of the project to define the scope, estimate costs and organize Gantt schedules. Once the WBS is developed, resources and responsibilities must be assigned.

The OBS provides an organizational rather than a task-based perspective of the project.  The hierarchical structure of the OBS allows the aggregation of project information to higher levels.  When project responsibilities are defined, the OBS and WBS are merged. In using WBS and OBS, it is assured that all elements (scope) of a project will be assigned to a responsible organization.

To develop an OBS:

  1. Draw the organization structure of the project team.
  2. Include all team members.
  3. Identify any positions that still need to be filled.

For example, if an organization were building a new office complex, an OBS might include the Project Management Office at the top of the structure with Civil, Structural, Plumbing and Electrical feeding into the Project Management Office. Each of the responsible organizations would have a person responsible for that organization.



Resource Break Down Structure

In project management, the Resource Breakdown Structure (RBS) is a standardized list of personnel resources related by function and arranged in a hierarchical structure. The Resource Breakdown Structure standardizes the Departments personnel resources to facilitate planning and controlling of project work. It defines assignable resources such as personnel, from a functional point of view; it identifies "who" is doing the work. The total resources define the Top Level, and each subsequent level is a subset of the resource category (or level) above it. Each descending (lower) level represents an increasingly detailed description of the resource until small enough to be used in conjunction with the Work Breakdown Structure (WBS) to allow the work to be planned, monitored and controlled.


Product Break Down Structure  (PBS)


In project management, a product breakdown structure (PBS) is an exhaustive, hierarchical tree structure of components that make up an item, arranged in whole-part relationship.

A PBS can help clarify what is to be delivered by the project and can help build a work breakdown structure.

The PRINCE2 project management method mandates the use of product based planning, part of which is developing a product breakdown structure.

PBS of a computer (example):

  • Main unit
    • Housing
    • Motherboard
      • CPU
      • RAM chips
      • ...
    • FDD
    • HDD
    • Video card
    • Sound card
    • Network card
    • LPT port card
  • Monitor
    • CRT
    • Housing
    • Electronic components
  • Mouse
    • Body
    • Marble
    • Cable
  • Keyboard



Risk Break Down Structure  (RBS)


What is a "Risk Breakdown Structure?"

To better grasp when the project needs to receive special scrutiny, in other words, when risk might happen, a simple tool, the RBS, will prove extremely valuable. The RBS can also help the project manager and the risk manager better understand recurring risks, and concentrations of risk which would lead to issues that affect the status of the project.

Following the concept of the Work Breakdown Structure,  the Risk Breakdown Structure provides a means for the project manager and risk manager to provide a means of structuring the risks being addressed and/or tracked. Just as PMI defines the Work Breakdown Structure as a "deliverable-oriented grouping of project elements that organizes and defines the total work scope of the project..." the RBS could be considered as a "a hierarchically organized depiction of the identified project risks arranged by risk category.

 Many project managers and risk managers currently use "home-grown" methods for listing, identifying, assessing, and tracking risks in their projects. These methods include spread-sheets, listing, generic risk taxonomy, based somewhat loosely on various standards and guidelines.

Simply putting the risks in a list or a simple table or even in a database does not provide the strength of using a structured, organized method similar to a Work Breakdown Structure. To fully understand the risks and therefore to better identify and assess the risk, a "deep-dive" into each risk taking as many levels of identification as necessary may be required. The project value of placing risks in a structure such as this lies in the ability of the project manager and risk manager to then quickly and easily identify and assess the risk, identify the potential risk triggers and develop a more robust risk response plan   If all risks are placed in a hierarchical structure as they are identified, and the structure is organized by source, the total risk exposure to the project can be more easily understood, and planning for the risk more easily accomplished.

Cost breakdown structure (CBS)

Classification of costs within a company or project into cost units/cost centers and cost elements/cost types. The establishment of a cost structure aids efficient cost planning, controlling, and the introduction of measures to reduce costs




2 comments on "Article - Break Down Structures - WBS OBS RBS PBS CBS an Overview"
  Commented by  Jean-Yves Moine, Freelancer, Project Management Consulting    | 06 15 2013 15:02:25 +0000
My vision of the xBS is quite different, for me WBS has 3 dimensions (ZBS, PBS and ABS), and OBS/RBS is another dimension crossed in the RAM in 3D (the project cube). There is also the time or the fifht dimension:

Best regards, Jean-Yves Moine
  Commented by  Samir Das, Tech Architect, Infosys    | 07 01 2009 07:34:41 +0000
Yes a breakdown structure which is a chart in which the critical work elements like tasks of a project are illustrated to portray their relationships to each other and to the project as a whole. And this graphical nature of the all the Breakdown structures can help a project manager predict outcomes based on various scenarios, which can ensure that optimum decisions are made about whether or not to adopt suggested procedures or the necessary changes.
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