Overview

Via Wikipedia

A work-breakdown structure (WBS)[2] in project management and systems engineering is a deliverable-oriented breakdown of a project into smaller components. A work breakdown structure is a key project deliverable that organizes the team's work into manageable sections. The Project Management Body of Knowledge (PMBOK 5) defines the work-breakdown structure as a "hierarchical decomposition of the total scope of work to be carried out by the project team to accomplish the project objectives and create the required deliverables." A work-breakdown structure element may be a product, data, service, or any combination of these. A WBS also provides the necessary framework for detailed cost estimation and control while providing guidance for schedule development and control.[3]

Key Differentiators

The WBS is organized around the primary products of the project (or planned outcomes) instead of the work needed to produce the products (planned actions).

Benefits

Ways To Breakdown

Value
Deliverables
Phases
Work Packages
Outcomes

Output

Program
Project
Contract

How To

Get clear on the end objective
Successively subdivide it into manageable components in terms of size, duration, and responsibility (e.g., systems, subsystems, components, tasks, subtasks, and work packages) which include all steps necessary to achieve the objective.

Visual

Horizontally in outline form
Vertically as a tree structure (like an organization chart).

Step Components

Description
Tasks
Materials
Cost

History

1957

The concept of work breakdown structure developed with the Program Evaluation and Review Technique (PERT) by the United States Department of Defense (DoD). PERT was introduced by the U.S. Navy in 1957 to support the development of its Polaris missile program.[7] While the term "work breakdown structure" was not used, this first implementation of PERT did organize the tasks into product-oriented categories.

1968

“DoD issued "Work Breakdown Structures for Defense Material Items" (MIL-STD-881), a military standard requiring the use of work breakdown structures across the DoD.[11]

1987

“In 1987, the Project Management Institute (PMI) documented expanding these techniques across non-defense organizations. The Project Management Body of Knowledge (PMBOK) Guide provides an overview of the WBS concept, while the "Practice Standard for Work Breakdown Structures" is comparable to the DoD standard but is intended for more general application.[13]”

Design Principles

100% rule

An important design principle for work breakdown structures is called the 100% rule.[14] It has been defined as follows:

The 100% rule states that the WBS includes 100% of the work defined by the project scope and captures all deliverables – internal, external, interim – in terms of the work to be completed, including project management. The 100% rule is one of the most important principles guiding the development, decomposition, and evaluation of the WBS. 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... It is important to remember that the 100% rule also applies to the activity level. The work represented by the activities in each work package must add up to 100% of the work necessary to complete the work package

—Wikipedia

Mutually exclusive elements

There must be no overlap in scope definition between different elements of a work breakdown structure. This ambiguity could result in duplicated work or miscommunications about responsibility and authority. Such overlap could also confuse project cost accounting. If the WBS element names are ambiguous, a WBS dictionary can help clarify the distinctions between WBS elements. The WBS Dictionary describes each component of the WBS with milestones, deliverables, activities, scope, and sometimes dates, resources, costs, quality.

Plan outcomes, not actions

If the work breakdown structure designer attempts to capture any action-oriented details in the WBS, the designer will likely include either too many actions or too few actions. Too many actions will exceed 100% of the parent's scope, and too few will fall short of 100% of the parent's scope. The best way to adhere to the 100% rule is to define WBS elements in terms of outcomes or results, not actions. This also ensures that the WBS is not overly prescriptive of methods, allowing for greater ingenuity and creative thinking on the part of the project participants. For new product development projects, the most common technique to ensure an outcome-oriented WBS is to use a product breakdown structure. Feature-driven software projects may use a similar technique which is to employ a feature breakdown structure. When a project provides professional services, a common technique is to capture all planned deliverables to create a deliverable-oriented WBS.[16] Work breakdown structures that subdivide work by project phases (e.g. preliminary design phase, critical design phase) must ensure that phases are clearly separated by a deliverable also used in defining entry and exit criteria (e.g., an approved preliminary or critical design review).

Level of detail

One must decide when to stop dividing work into smaller elements. For most projects a hierarchy of two to four levels will suffice.[17] This will assist in determining the duration of activities necessary to produce a deliverable defined by the WBS. There are several heuristics or "rules of thumb" used when determining the appropriate duration of an activity or group of activities necessary to produce a specific deliverable defined by the WBS.

The first is the "80-hour rule" which means that no single activity or group of activities at the lowest level of detail of the WBS to produce a single deliverable should be more than 80 hours of effort.
The second rule of thumb is that no activity or group of activities at the lowest level of detail of the WBS should be longer than a single reporting period. Thus if the project team is reporting progress monthly, then no single activity or series of activities should be longer than one month long.
The last heuristic is the "if it makes sense" rule. Applying this rule of thumb, one can apply "common sense" when creating the duration of a single activity or group of activities necessary to produce a deliverable defined by the WBS.

A work package at the activity level is a task that:

can be realistically and confidently estimated;
makes no sense practically to break down any further;
can be completed in accordance with one of the heuristics defined above;
produces a deliverable which is measurable; and
forms a unique package of work that can be outsourced or contracted out.

Coding scheme

It is common for work breakdown structure elements to be numbered sequentially to reveal the hierarchical structure. The purpose of the numbering is to provide a consistent approach to identifying and managing the WBS across like systems regardless of vendor or service.[18] For example, 1.1.2 Propulsion (in the example below) identifies this item as a Level 3 WBS element, since there are three numbers separated by two decimal points. A coding scheme also helps WBS elements to be recognized in any written context and allows for mapping to the WBS Dictionary.[19]

A practical example of the WBS coding scheme is[20]

Terminal element

The lowest element in a tree structure, a terminal element, is one that is not further subdivided. In a Work Breakdown Structure such elements (activity or deliverable), also known as work packages, are the items that are estimated in terms of resource requirements, budget and duration; linked by dependencies; and schedule. At the juncture of the WBS element and organization unit, control accounts and work packages are established, and performance is planned, measured, recorded, and controlled.[21] A WBS can be expressed down to any level of interest. Three levels are the minimum recommended, with additional levels for and only for items of high cost or high risk,[22] and two levels of detail at cases such as systems engineering or program management,[23] with the standard showing examples of WBS with varying depth such as software development at points going to 5 levels[24] or fire-control system to 7 levels.[25]

Consistent to norms

The higher WBS structure should be consistent with whatever norms or template mandates exist within the organization or domain. For example, shipbuilding for the U.S. Navy must respect that the nautical terms and their hierarchy structure put into MIL-STD[26] are embedded in Naval Architecture[27] and that matching Navy offices and procedures have been built to match this naval architecture structure, so any significant change of WBS element numbering or naming in the hierarchy would be unacceptable.

Related Words

System breakdown structure