The Work Breakdown Structure (WBS), with Examples

Hierarchical Work Structure (WBS) (in English: Work Breakdown Structure, WBS; sometimes Structural Decomposition of Work, WBS) — is a hierarchical breakdown of all the work that must be performed to achieve the goals of the project into smaller operations and actions, down to a level at which the ways of carrying out these actions are entirely clear and the corresponding work can be estimated and scheduled. It also includes defining the intermediate results of all the components that make up this work structure.

Project planning is based on compiling a structured list of works, the completion of which makes it possible to achieve the goals of the project. For this purpose a tool is used that is known under several names:

• in English – Work Breakdown Structure (or the WBS structure)
• in Russian – structural decomposition of project work (SDW) or hierarchical work structure (HWS).

The essence of decomposition lies in dividing (breaking down) the process into parts according to some criterion or another: by the type of product produced during the work, by functionality, by life-cycle stage, etc. It is important that such a division identify sufficiently simple components – more manageable elements that help to better control the execution of tasks and the achievement of the goal. However, the work breakdown structure differs from a simple implementation schedule, from a document resembling a project plan, and from a list of milestones.

The WBS is intended for detailed planning, cost estimation and ensuring the personal responsibility of those performing the work.

Relationship of the WBS with the main types of project structures

• Information structure
• Organization Breakdown Structure (organizational structure)
• AccountBreakdown Structure(structure of cost items)
• ResourceBreakdown Structure(resource structure)
• Milestone structure
• Functional structure

Basic terms and definitions

Work — continuous physical or mental effort directed at overcoming obstacles and achieving goals or results; a specific task, duty, function or assignment, often being part of a phase or of other, larger-scale work; something produced or accomplished as a result of effort or the application of skills (qualifications).

Breakdown — division into parts or categories, the identification of simple components.

Structure — a fixed ordered set of objects and the relations between them, the classification of something according to a given criterion.

These definitions mean that the work breakdown structure has the following characteristics:

• It describes, with the necessary precision, the content of the project's work.
• It defines the entire scope of the project's work.
• It is formed as a hierarchical structure (the project is decomposed into packages/sub-packages, etc. of work).
• It represents the scope of work for a package as a list of works having a measurable or comparable result.
• It has an objective or measurable result, which is regarded as the result of the work on the package or the aggregate of the results of the works.

WBS - is a hierarchical and phased decomposition of the project into phases, deliverables and work packages. It is a tree-like structure that shows the subdivision of the effort required to achieve the goal; for example, a programme, a project and a contract. In a project or contract, the WBS is developed starting from the final goal and successively dividing it into manageable components in terms of size, duration and responsibility (for example, systems, subsystems, components, tasks, subtasks and work packages), which include all the steps necessary to achieve the goal.

The work breakdown structure provides a common framework for the natural development of overall contract planning and control, and serves as the basis for dividing the work into definable increments from which a statement of work, schedule, cost and labour-hours. reporting can be established.

The work breakdown structure makes it possible to sum up the subordinate costs of tasks, materials, etc. into their successively higher “parent” tasks, materials, etc. For each element of the work breakdown structure a description of the task that needs to be performed is created . This method (sometimes called system structure trial ) is used to define and organise the overall scope in the form of a project .

The WBS is organized around the main deliverables of the project (or the planned results) rather than the work required to produce the deliverables (the planned activities). Since the planned results are the desired goals of the project, they form a relatively stable set of categories in which the costs of the planned activities necessary 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 cost-accounting function, the WBS also helps to map requirements from one level of the system specification to another, for example a cross-reference matrix mapping functional requirements onto upper- or lower-level design documents. The WBS can be displayed horizontally in outline form or vertically as a tree structure (for example, an organizational chart).

Development of the WBS usually takes place at the start of the project and precedes detailed project and task planning.

Definition and characteristics of the WBS

The work breakdown structure (Work Breakdown Structure) is the term for a representation of the project executed in the form of a hierarchical work structure, which is achieved by means of sequential decomposition. The tool is aimed at detailed planning, cost estimation, defining and allocating the personal responsibility of the performers, etc. – that is, at the main works and results that define the content of the project.

In a Work Breakdown Structure the elements of the project can be a service, a product, a piece of work, or a group of works (wbs group). Each lower level in the hierarchy details some element of the level above it, but the following principles must be observed:

1. The “Correct Tree” principle. The idea is that each dependent element (each “branch”, or, with an even finer subdivision, each “leaf”) should have only one parent element.
2. The principle of completeness and logical coherence. All elements of the project must be accounted for in the WBS, but nothing should be duplicated.
3. The principle of a single criterion. The decomposition process must proceed according to a single criterion, so, for example, one cannot work simultaneously and interchangeably with both the product and functional tasks.
4. The principle of WBS depth. Division should be carried out until the resulting structure is easily manageable and controllable. Most often this process ends when structuring reaches the level of an elementary piece of work – one that a single employee is able to perform, or that can be controlled as a separate unit.

Implementing these principles in a project results in the work breakdown structure acquiring certain characteristics, namely:

• it always describes the content of the works with the necessary (sufficient) precision,
• it covers the entire scope – 100% – of the project's work (if any works are not included in the WBS, then they also fall out of the content),
• the structure is decomposed into hierarchically arranged elements (packages, sub-packages, etc.)., with the upper levels corresponding to the main stages of the project, and as one approaches the lower levels the definition of the works becomes ever more detailed,
• the work blocks in the structure are autonomous,
• the works have a measurable (or comparable) result, and each work block has an original result (in which case time and expenses are easily estimated),
• the starting and finishing activities are defined clearly and unambiguously.

Thus, each successive level of decomposition progressively details the content of the project, which makes it possible to estimate the volumes of work performed, the amount of money absorbed, and the implementation timelines.

In this case, the lower levels of the work packages correspond to relatively small volumes of work, which simplifies the estimation of performance parameters and also helps to clearly define the actions leading to the achievement of the project goals. This approach forms the basis for establishing cost and labour intensity as measurable indicators.

Principles for constructing a Hierarchical Work Structure (HWS) (Work Breakdown Structure, WBS)

The 100% Rule

An important principle for designing the work breakdown structure 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 for developing, decomposing and evaluating the WBS. The rule is applied 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.^[15]

Mutually exclusive elements

Mutually exclusive: in addition to the 100% rule, it is important that there be no overlap in the definition of scope between the different elements of the work breakdown structure. This ambiguity can lead to duplication of work or to misunderstandings about responsibility and authority. Such overlap can also cause confusion with respect to project cost accounting. If the names of the WBS elements are ambiguous, a WBS dictionary can help clarify the differences between the WBS elements. The WBS dictionary describes each WBS component together with its key milestones, deliverables, activities, scope, and sometimes dates, resources, costs and quality.

Plan deliverables, not activities

If the developer of the work breakdown structure attempts to capture any activity-oriented details in the WBS, they will most likely include either too many activities or too few activities. Too many activities will exceed 100% of the parent scope, while too few will fall below 100% of the parent scope. The best way to adhere to the 100% rule is to define WBS elements in terms of outcomes or results, rather than actions. This also ensures that the WBS does not overly prescribe methods, which allows project participants to exercise greater ingenuity and creative thinking. For new product development projects, the most common method of ensuring a results-oriented WBS is to use a product breakdown structure. Software projects based on features can use a similar method, which consists in using a feature breakdown structure. When a project delivers professional services, the common method is to capture all the planned deliverables in order to create a WBS oriented towards the final result. Work breakdown structures that divide the work by project phase (for example, the preliminary design phase, the critical design phase) must provide a clear division of the phases by deliverables, which are also used when defining entry and exit criteria (for example, an approved preliminary or critical design review). .

Level of detail

A decision must be made as to when to stop breaking the work down into smaller elements. For most projects a hierarchy of two to four levels is sufficient. ^[17] This will help in determining the duration of the activities needed to produce the deliverables 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 needed to produce a specific deliverable defined by the WBS.

• The first is the “80-hour rule”, which means that no activity or group of activities at the lowest level of detail of the WBS for producing a single deliverable should take 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 last longer than a single reporting period. Thus, if the project team reports on progress monthly, then no activity or series of activities should last longer than one month.
• The last heuristic is the “if it makes sense” rule. By applying this rule of thumb, one can apply “common sense” when establishing the duration of an individual activity or group of activities needed to produce the final deliverable defined by the WBS.

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

• can be realistically and confidently estimated;
• there is practically no point in breaking down further;
• can be completed in accordance with one of the heuristics defined above;
• produces a measurable result; and
• forms a unique work package that can be outsourced or subcontracted.

Coding scheme

Usually the elements of the work breakdown structure are numbered sequentially in order to reveal the hierarchical structure. The purpose of the numbering is to provide a uniform approach to identifying and managing the WBS across identical systems, regardless of the vendor or service. ^[18] For example, 1.1.2 Propulsion (in the example below) identifies this element as a level-3 WBS element, since there are three numbers separated by two decimal points. The coding scheme also helps to recognize WBS elements in any written context and makes it possible to map them into a WBS dictionary. ^[19]

A practical example of a WBS coding scheme

1.0 Aviation System

1.1 Air Vehicle1.1.1 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 Systems 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

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 (an activity or a deliverable), also known as work packages, are elements that are estimated in terms of resource needs, budget, and duration; are linked by dependencies; and are scheduled. At the intersection of a WBS element and an organizational unit, control accounts and work packages are created, and performance is planned, measured, recorded, and controlled there. ^[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, high-cost or high-risk items and two levels of detail in cases such as systems engineering or program management, ^[23] with the standard showing examples of WBSs of varying depth, for example software development broken down to as many as 5 levels ^[24] or a fire-control system down to 7 levels. ^[25]

Conforms to Standards

A higher-level WBS structure must conform to any standards or templates existing within the organization or domain. For example, U.S. Navy shipbuilding must take into account that naval terms and their hierarchical structure, set out in MIL-STD ^[26] , are embedded in naval architecture ^[27], and that the corresponding Navy offices and procedures were built in accordance with this naval architecture structure, so any substantial change to the numbering or naming of WBS elements in the hierarchy would be unacceptable.

Algorithm for Building a Work Breakdown Structure

In practice, in the process of forming a Work Breakdown Structure one must be able to ask the right questions and organize the structuring process competently. To this end, various algorithmic options are proposed at the initial stage, describing a top-down method of creating a WBS.

Example No. 1:

• Taking the definition of the project scope as a basis, the project goals are written out.
• In a row (horizontally), the initial deliverables needed to achieve the goals are listed.
• For each individual initial deliverable, the work or key blocks required to produce it are determined.
• In a vertical column, they are broken down to the necessary level of detail.
• Team members and all stakeholders are involved in the project work. (Alternatively – the WBS is developed at once through the joint efforts of the participants).

Example No. 2 using sticky notes and a flip chart:

• Project participants working as a team need to be asked what, in their opinion, is needed to implement the project.
• All the answers to this question are written down by project participants on sticky notes.
• Similar and matching answers about the most significant tasks are grouped into stacks or posted on a display board in thematic columns.
• Tasks that do not fit into any column are stuck on separately.
• The columns or stacks of grouped tasks are given names, which are written on the flip chart (with the corresponding set of sticky notes under each category).

Next, the final deliverables are broken down into operations, and this cycle continues until it becomes possible to track and control individual tasks. It is important that one work package contain one deliverable.

If project management software is used to create the Work Breakdown Structure – for example, the most common one, MS Project, or its equivalents – then:

• The final project goal is entered in the task name field.
• After the final deliverables have been evaluated and listed, all sub-deliverables are shifted to the right, so that their set forms one final deliverable.
• The final deliverables are broken down into operations. For each sub-deliverable its own list of operations is drawn up. This action is repeated until the work-package level is reached. In doing so, the rightward shift creates links between deliverables and their sub-deliverables. (MS Project creates the WBS code automatically in the outline-number field, which changes when a task moves to a different level).

To embed the WBS into the project schedule, the following information needs to be added to the previously created hierarchical structure:

• Duration, or the total time to complete each task.
• The dependency and relationship between tasks, which can be established using a network diagram.
• Constraints for each task (if any).
• Start and end dates for the task (if the duration parameter is specified, the program calculates these dates automatically).
• Resource names.

Since work decomposition can be carried out according to different criteria, it is important to ensure that the chosen criterion-based approach necessarily covers the entire scope of the project. A mixed approach is sometimes used, in which different decomposition criteria are chosen at different levels: at the first – life-cycle phases, at the second – organizational structures, at the third – key deliverables.

WBS as a Management Tool in Various Project Manifestations

The structural decomposition tool can be effectively applied in various project manifestations:

• To define project deliverables.
• To organize communications. The WBS helps carry out the targeted transfer of information, taking into account the task and the participant's responsibility for its execution.
• To support documentation and reporting. The documentary reflection of the WBS is expressed in common terminology, in top-down budget formation, and in the preparation of separate reporting that corresponds to the WBS structure.
• To optimize management and standardize levels. Thus the specialized literature recommends using no more than 6 levels, where the top 3 are intended for customer-level information and the bottom 3 for contractor-level information. However, first and foremost, the depth of detail should be oriented toward the complexity and size of the project.

A work breakdown structure can either be developed “from scratch” or include components of previously created WBS structures, taken from earlier similar projects or from standardized template variants used by the organization based on their proven success in typical conditions in the past.

Main Types of WBS with Examples:

• -Product-based when the project is broken down by the elements of the project's product
• -Functional decomposition by functional areas of management
• -Organizational
• -Other (by life-cycle phases, by contracts, by subcontractors, etc.)
• -Mixed

“Product-based” WBS- construction of the WBS by components of the project's product. The elements chosen for the WBS are the product elementsof the project, its tangible deliverables. To name the work packages and individual work items, nouns are used.

“Functional” WBS- construction of the WBS by functional elements of activity. The elements chosen for the WBS are the elements of the operations of the project's production technology cycle, grouped by functional characteristic. To name the work packages and individual work items, mainly nouns are used.

“Organizational” WBS- construction of the WBS by elements of the organizational structure. The elements chosen for the WBS are the elements of the organizational structure or of the organization's structural chart. To name the work packages and individual work items, mainly nouns- the names of functional units - are used

By phases of the project life cycle

Systems Approach to the WBS

• A project is a process of transforming input elements (resources, money, labor costs) into output elements (project deliverables).
• Input elements –that which the performer of an elementary work item must obtain from some source, internal or external, in relation to the project.
• Output elements –that which must be transferred to some other part of the project, or that which is part of the project's deliverables.
• It is necessary to add work items for preparing the required input elements that were not obtained from internal or external sources.
• It is necessary to exclude redundant work. Their hallmark is output elements that cannot be transferred to other components of the project and are not deliverables of the project.
• It is necessary to exclude elementary work items that duplicate one another, when the person responsible for performing the work finds more than one work item to provide the same output elements.

WBS by Various Bases

WBS by performers

Difficulties in Developing a WBS

• Finding a balance between the level of project detail and the requirements for collecting actual information and reporting (excessive detail).
• Developing WBS elements that define only the project stages or the organizational structure without taking into account intermediate project deliverables (insufficient detail).
• Insufficient attention to developing the WBS and moving directly on to forming the network schedule

See Also

• [[b147]]
• Anatomy of a Project
• Project Management Software
• Project Planning
• Structure Diagram
• MECE Principle
• Time Blocking
• Calendar Plan
• network diagram
• Information Structure
• Organization Breakdown Structure (organizational structure)
• AccountBreakdown Structure(structure of cost items)
• ResourceBreakdown Structure(structure of resources)
• Milestone Structure
• Functional Structure
• responsibility matrix

See also

• Simulation Planning. Gann Chart. network planning model. Project