Work breakdown structure - AbsoluteAstronomy.com

A work breakdown structure (WBS), in project management

Project management

Project management is the discipline of planning, organizing, securing, and managing resources to achieve specific goals. A project is a temporary endeavor with a defined beginning and end , undertaken to meet unique goals and objectives, typically to bring about beneficial change or added value...

and systems engineering

Systems engineering

Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...

, is a deliverable oriented decomposition of a project into smaller components. It defines and groups a project

Project

A project in business and science is typically defined as a collaborative enterprise, frequently involving research or design, that is carefully planned to achieve a particular aim. Projects can be further defined as temporary rather than permanent social systems that are constituted by teams...

's discrete work elements in a way that helps organize and define the total work scope of the project.

A work breakdown structure element may be a product

Product (business)

In general, the product is defined as a "thing produced by labor or effort" or the "result of an act or a process", and stems from the verb produce, from the Latin prōdūce ' lead or bring forth'. Since 1575, the word "product" has referred to anything produced...

, data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

, 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.

Overview

The work breakdown structure is a tree structure

Tree structure

A tree structure is a way of representing the hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the classic representation resembles a tree, even though the chart is generally upside down compared to an actual tree, with the "root" at the top and the...

, which shows a subdivision of effort required to achieve an objective; for example a program

Program management

Program management or programme management is the process of managing several related projects, often with the intention of improving an organization's performance...

, project

Project

, and contract

Contract

A contract is an agreement entered into by two parties or more with the intention of creating a legal obligation, which may have elements in writing. Contracts can be made orally. The remedy for breach of contract can be "damages" or compensation of money. In equity, the remedy can be specific...

.

In a project or contract, the WBS is developed by starting with the end objective and successively subdividing 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.

The work breakdown structure provides a common framework for the natural development of the overall planning and control of a contract and is the basis for dividing work into definable increments from which the statement of work

Statement of work

A statement of work is a formal document that captures and defines the work activities, deliverables and timeline a vendor will execute against in performance of specified work for a client...

can be developed and technical, schedule, cost, and labor hour reporting can be established.

A work breakdown structure permits summing of subordinate costs for tasks, materials, etc., into their successively higher level “parent” tasks, materials, etc. For each element of the work breakdown structure, a description of the task to be performed is generated. This technique (sometimes called a system breakdown structure ) is used to define and organize the total scope

Scope (project management)

In project management, the term scope has two distinct uses: Project Scope and Product Scope.Project Scope"The work that needs to be accomplished to deliver a product, service, or result with the specified features and functions."Product Scope...

of a project

Project

.

The WBS is organised around the primary products of the project (or planned outcomes) instead of the work needed to produce the products (planned actions). Since the planned outcomes are the desired ends of the project, they form a relatively stable set of categories in which the costs of the planned actions needed to achieve them can be collected. A well-designed WBS makes it easy to assign each project activity to one and only one terminal element of the WBS. In addition to its function in cost accounting, the WBS also helps map requirements from one level of system specification to another, for example a requirements cross reference matrix mapping functional requirements to high level or low level design documents.

History

The concept of work breakdown structure developed with the Program Evaluation and Review Technique

Program Evaluation and Review Technique

The Program ' Evaluation and Review Technique, commonly abbreviated PERT, is a statistical tool, used in project management, that is designed to analyze and represent the tasks involved in completing a given project...

(PERT) in the United States Department of Defense

United States Department of Defense

The United States Department of Defense is the U.S...

(DoD). PERT was introduced by the U.S. Navy in 1957 to support the development of its Polaris

UGM-27 Polaris

The Polaris missile was a two-stage solid-fuel nuclear-armed submarine-launched ballistic missile built during the Cold War by Lockheed Corporation of California for the United States Navy....

missile program. While the term "work breakdown structure" was not used, this first implementation of PERT did organize the tasks into product-oriented categories.

By June 1962, DoD, NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

and the aerospace industry published a document for the PERT/COST system which described the WBS approach. This guide was endorsed by the Secretary of Defense for adoption by all services. In 1968, the DoD issued "Work Breakdown Structures for Defense Materiel Items" (MIL-STD-881), a military standard requiring the use of work breakdown structures across the DoD. This standard established top-level templates for common defense materiel

Materiel

Materiel is a term used in English to refer to the equipment and supplies in military and commercial supply chain management....

items along with associated descriptions (WBS dictionary) for their elements.

The document has been revised several times, most recently in 2011. The current version of this document can be found in "Work Breakdown Structures for Defense Materiel Items" (MIL-STD-881C). It includes standards for preparing work breakdown structures, templates for the top three levels of typical systems, and a set of "common elements" that are applicable to all major systems and subsystems.

Defense Materiel Item categories from MIL-STD-881C:

Aircraft Systems WBS
Electronic Systems WBS
Missile Systems WBS
Ordnance Systems WBS
Sea Systems WBS
Space Systems WBS
Surface Vehicle Systems WBS
Unmanned Air Vehicle Systems WBS
Unmanned Maritime Systems WBS
Launch Vehicle Systems WBS
Automated Information Systems WBS

The common elements identified in MIL-STD-881C, Appendix L are: Integration, assembly, test, and checkout; Systems engineering; Program management; System test and evaluation; Training; Data; Peculiar support equipment; Common support equipment; Operational and site activation; Industrial facilities; Initial spares and repair parts. The standard also includes additional common elements unique to Space Systems, Launch Vehicle Systems and Automated Information Systems.

In 1987, the Project Management Institute

Project Management Institute

The Project Management Institute is a not-for-profit professional organization for the project management profession with the purpose of advancing project management.- Overview :...

(PMI) documented the expansion of 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 handbook, but is intended for more general application.

100% rule

One of the most important work breakdown structure design principles is called the 100% rule. 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 deliverable

Deliverable

Deliverable is a term used in project management to describe a tangible or intangible object produced as a result of the project that is intended to be delivered to a customer . A deliverable could be a report, a document, a server upgrade or any other building block of an overall project.A...

s – 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.

Mutually exclusive elements

Mutually exclusive

In layman's terms, two events are mutually exclusive if they cannot occur at the same time. An example is tossing a coin once, which can result in either heads or tails, but not both....

: In addition to the 100% rule, it is important that there is no overlap in scope definition between two elements of a work breakdown structure. This ambiguity could result in duplicated work or mis-communications about responsibility and authority. Such overlap could also cause confusion regarding 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, he/she 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. It is considered that the best way to adhere to the 100% rule is to define WBS elements in terms of outcomes or results. 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

Product breakdown structure

In project management, a product breakdown structure is a tool for analysing, documenting and communicating the outcomes of a project, and forms part of the product based planning technique....

. Feature-driven software projects

Feature Driven Development

Feature-driven development is an iterative and incremental software development process. It is one of a number of Agile methods for developing software and forms part of the Agile Alliance. FDD blends a number of industry-recognized best practices into a cohesive whole. These practices are all...

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. 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

Exit-criteria

Exit criteria are the criteria or requirements which must be met to complete a specific process.For example for Fagan Inspection the low-level document must comply with specific exit-criteria before the development process can be taken to the next phase.In telecommunications, when testing new...

(e.g. an approved preliminary or critical design review document).

Level of detail

A question to be answered in determining the duration of activities necessary to produce a deliverable defined by the WBS is when to stop dividing work into smaller elements. 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 to produce a single deliverable should be more than 80 hours of effort.
The second rule of thumb is that no activity or series of activities 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 which 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 for the numbering is to provide a consistent approach to identifying and managing the WBS across like systems regardless of vendor or service. 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 a decimal point

Decimal separator

Different symbols have been and are used for the decimal mark. The choice of symbol for the decimal mark affects the choice of symbol for the thousands separator used in digit grouping. Consequently the latter is treated in this article as well....

. A coding scheme also helps WBS elements to be recognized in any written context.

A practical example of the WBS coding scheme is

1.0 Aircraft System

1.1 Air Vehicle

1.1.1 Airframe

1.1.1.1 Airframe Integration, Assembly, Test and Checkout

1.1.1.2 Fuselage

1.1.1.3 Wing

1.1.1.4 Empennage

1.1.1.5 Nacelle

1.1.1.6 Other Airframe Components 1..n (Specify)

1.1.2 Propulsion

1.1.3 Vehicle Subsystems

1.1.4 Avionics

1.2 System Engineering

1.3 Program Management

1.4 System Test and Evaluation

1.5 Training

1.6 Data

1.7 Peculiar Support Equipment

1.8 Common Support Equipment

1.9 Operational/Site Activation

1.10 Industrial Facilities

1.11 Initial Spares and Repair Parts

An example in the software industry would be as follows:

1267.1 Systems Integration

1267.1.1 Requirements Definition

1267.1.2 Regulations

1267.1.3 Scheduling

1267.1.4 Monitoring & Control

1267.1.5 Procurement Management

1267.1.6 Closeout

1267.2 Design

1267.2.1 Conceptual Design

1267.2.2 Preliminary Design

1267.2.3 Final Design

Terminal element

A terminal element is the lowest element (activity or deliverable

Deliverable

) in a work breakdown structure; it is not further subdivided. Terminal elements are the items that are estimated

Estimation

Estimation is the calculated approximation of a result which is usable even if input data may be incomplete or uncertain.In statistics,*estimation theory and estimator, for topics involving inferences about probability distributions...

in terms of resource requirements

Resource management

In organizational studies, resource management is the efficient and effective deployment of an organization's resources when they are needed. Such resources may include financial resources, inventory, human skills, production resources, or information technology...

, budget

Budget

A budget is a financial plan and a list of all planned expenses and revenues. It is a plan for saving, borrowing and spending. A budget is an important concept in microeconomics, which uses a budget line to illustrate the trade-offs between two or more goods...

and duration

Duration (project management)

Duration of a project's terminal element is the number of calendar periods it takes from the time the execution of element starts to the moment it is completed.Do not confuse duration with work. E.g...

; linked by dependencies

Dependency (project management)

In a project network, a dependency is a link amongst a project's terminal elements.There are four kinds of dependencies with respect to ordering terminal elements :# Finish to start...

; and scheduled

Schedule (project management)

In project management, a schedule consists of a list of a project's terminal elements with intended start and finish dates. Terminal elements are the lowest element in a schedule, which is not further subdivided...

. At the juncture of the WBS element and organization unit, control accounts and work package

Work package

In project management, a work package is a subset of a project that can be assigned to a specific part for execution. Because of the similarity, work packages are often misidentified as projects....

s are established and performance is planned, measured, recorded, and controlled.

Example

The figure on the right shows a work breakdown structure construction technique that demonstrates the 100% rule and the "progressive elaboration" technique. At WBS Level 1 it shows 100 units of work as the total scope of a project to design and build a custom bicycle. At WBS Level 2, the 100 units are divided into seven elements. The number of units allocated to each element of work can be based on effort or cost; it is not an estimate of task duration.

The three largest elements of WBS Level 2 are further subdivided at Level 3. The two largest elements at Level 3 each represent only 17% of the total scope of the project. These larger elements could be further subdivided using the progressive elaboration technique described above.

WBS design can be supported by software (e.g. a spreadsheet

Spreadsheet

A spreadsheet is a computer application that simulates a paper accounting worksheet. It displays multiple cells usually in a two-dimensional matrix or grid consisting of rows and columns. Each cell contains alphanumeric text, numeric values or formulas...

) to allow automatic rolling up of point values. Estimates of effort or cost can be developed through discussions among project team members. This collaborative technique builds greater insight into scope definitions, underlying assumptions, and consensus regarding the level of granularity required to manage the project.

Misconceptions

A WBS is not an exhaustive list of work. It is instead a comprehensive classification of project scope.
A WBS is neither a project plan
Project plan
A project plan, according to the Project Management Body of Knowledge, isPRINCE2 defines:In some industries, particularly information technology, the term "project plan" can refer to a Gantt chart or other document that shows project activities along a timeline. While common, this use is inaccurate...

, a schedule
Schedule (project management)
In project management, a schedule consists of a list of a project's terminal elements with intended start and finish dates. Terminal elements are the lowest element in a schedule, which is not further subdivided...

, nor a chronological listing. It specifies what will be done, not how or when.
A WBS is not an organizational hierarchy, although it may be used when assigning responsibilities. See also: responsibility assignment (RACI) matrix
Responsibility assignment matrix
A responsibility assignment matrix , also known as RACI matrix or Linear Responsibility Chart , describes the participation by various roles in completing tasks or deliverables for a project or business process...

(also called a Staffing Matrix).

Overview

History

100% rule

Mutually exclusive elements

Plan outcomes, not actions

Level of detail

Coding scheme

Terminal element

Example

Misconceptions

See also

Further reading