100% rule An important design principle for work breakdown structures 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 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.
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. 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).
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 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
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.
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." 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
milestones, deliverables, activities, scope, and sometimes dates,
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."
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. 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, such as progress tracking, scheduling, or billing, and allows for mapping to the WBS Dictionary. 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
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 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. 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, and two levels of detail at cases such as systems engineering or program management, with the standard showing examples of WBS with varying depth such as software development at points going to 5 levels or fire-control system to 7 levels.
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 are embedded in Naval Architecture 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. == Example ==