Editing Work breakdown structure (section)

==Design principles==

===  100% rule ===
An important design principle for work breakdown structures is called the 100% rule.<ref>''Effective Work Breakdown Structures'' By Gregory T. Haugan, Published by Management Concepts, 2001, {{ISBN|1567261353}}, p.17</ref> 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.<ref>''Practice Standard for Work Breakdown Structures (Second Edition)'', published by the [[Project Management Institute]], {{ISBN|1933890134}}, page 8</ref>

==== Mutually exclusive elements ====
[[Mutually exclusive]]: In addition to the 100% rule, 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.

===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. When a project provides professional services, a common technique is to capture all planned deliverables to create a deliverable-oriented WBS.<ref>Swiderski, Mark A., PMP [https://www.workbreakdownstructure.com/work-breakdown-structure-according-to-pmbok.php workbreakdownstructure.com], PMBOK-Work Breakdown Structures. Accessed 16. June 2013.</ref> 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]] (e.g., an approved preliminary or critical [[Design review (US Government)|design review]]).

====Product breakdown structure (PBS)====
For new product development projects, the most common technique to ensure an outcome-oriented WBS is to use a [[product breakdown structure]] (PBS).

====Feature-driven development====
[[Feature-driven development|Feature-driven software projects]] may use a similar technique as the WBS, which is to use a feature breakdown structure.

=== 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. 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 [[#Terminal element|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 [[#Terminal element|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.

==== Work package ====
According to the [[Project Management Institute]], a '''work package''' is the "lowest level of the work breakdown structure for which cost and duration are estimated and managed."{{sfn|Project Management Institute|2021|loc=§Glossary Section 3. Definitions}}

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.

==== WBS dictionary ====
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 [[Milestone (project management)|milestones]], deliverables, activities, scope, and sometimes dates, [[Resource (project management)|resources]], costs, quality.
According to the [[Project Management Institute]], the WBS dictionary is defined as a "document that provides detailed deliverable, activity, and scheduling information about each component in the work breakdown structure."
{{sfn|Project Management Institute|2021|loc=§Glossary Section 3. Definitions}}

====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.<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶4.3</ref> 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 separator|decimal points]]. A coding scheme also helps WBS elements to be recognized in any written context, such as progress tracking, scheduling, or billing, and allows for mapping to the WBS Dictionary.{{citation needed|date=April 2024}}  It is a preferred practice that the [[Statement of work]] or other contract descriptive include the same section terms and hierarchical structure as the WBS.

A practical example of the WBS coding scheme is<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011 Appendix A, ¶A.3</ref>

''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''

=== Terminal element ===
The lowest element in a [[Tree (data structure)|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 [[Estimation (project management)|estimated]] in terms of [[Resource management|resource requirements]], [[budget]] and duration; linked by [[Dependency (project management)|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.<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶3.1.4</ref> 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,<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶1.4.1</ref> and two levels of detail at cases such as systems engineering or program management,<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶2.2.4.2</ref> with the standard showing examples of WBS with varying depth such as software development at points going to 5 levels<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶Fig.3-6</ref> or fire-control system to 7 levels.<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶Fig.3-1</ref>

=== 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<ref>MIL-STD-881C, Work Breakdown Structures for Defense Materiel Items, 3 October 2011, ¶Appendix E</ref> are embedded in Naval Architecture<ref>{{cite book
 | last = Gilmer
 | first = Thomas
 | date = 1982-08-04
 | isbn = 9780870213182
 | title = Introduction to Naval Architecture
 | pages = 98
 | publisher = Naval Institute Press
 | url = https://books.google.com/books?id=_lF1DZ1OPJQC&q=%22work+breakdown+structure%22+wbs+navy+ship&pg=PA92}}</ref> 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.