Work Breakdown Structure
As described earlier, the process of project control requires the
establishment of a firm base line for the project. The base line
must be defined in terms of scope, cost, time and quality, on a
compatible basis. To be successful, the Project Manager must be
able to make use of this and all other available information. At
any point in time, he must be able to identify problems early to
minimize their effects.
Therefore, the scope of the project must be broken down into a
suitably coded structure that identifies manageable segments with
clearly assigned responsibilities. This is known as a project breakdown,
or Work Breakdown Structure (WBS), see Figures 6a,
b, and c for a typical
Figure 6a: Top level of a process plant project WBS
Figure 6b: Detailed WBS for the Conception and Definition phases
Figure 6c: Detailed WBS for the Execution and Transfer phases
Work Breakdown Structure - a task-oriented "family
tree" of activities, which organizes, defines, and graphically
displays the work to be accomplished.
A WBS must:
- Establish an information structure for describing the project's
- Serve as an effective means of communication to integrate the
objectives and activities of all the internal and external organizations
involved in the project;
- Represent the planning of the project, step by step;
- Separate sequential and parallel activities assigned to different
groups who will schedule, measure and control their own performance;
- Reflect the procurement strategy during the various stages of
the project's life cycle.
To be effective this WBS and corresponding coding requires:
- Early implementation;
- Flexibility and expandability;
- Universal application;
- Simplicity; and
- Capability of summation.
The "manageable segments" of the project referred to
above, are usually referred to as activity, commitment or Work Packages.
A Work Package describes the work to be performed by a specific
organizational unit, and serves as a vehicle for monitoring and
reporting on progress, cost and schedule. All work packages fall
into one of three different categories:
- Discrete Tasks which have a specific end result or objective.
These normally cover 60 to 75 percent of the total work in a project.
- Apportioned-effort Tasks which can be directly related and apportioned
to discrete tasks. Examples include quality control or inspection.
These tasks are required in support of the discrete tasks, and
hence, their schedule and budget can be related to the discrete
- Level-of-effort Tasks which have performance standards rather
than specific end results. These consist mainly of the overhead
accounts, e.g., management, administration, liaison, coordination,
etc. These tasks are characterized by relatively level, time-phased
budgets and are not time-limited as in the case of the discrete
Essential Work Package Rules
Note that a work package is a generic term describing the unit
at the lowest developed level of the relevant part of the WBS. The
distinction is made between the lowest developed level and the lowest
possible level, because at any given time not all work packages
will be classified at the same level. In other words, a work
package is not a distinct level in the Work Breakdown Structure.
To be effective, work packages should be controlled by the following
Rule 1: A work package must represent a unit of work at
a level where work is performed.
Rule 2: It must be clearly distinguishable from all other
Rule 3: It should have scheduled start and completion dates.
Rule 4: It should have a budget.
Rule 5: Its size and duration should be limited to relatively
short spans of time.
Rule 6: It must integrate with other work packages and schedules.
Rule 7: It must represent a level at which actual costs
can be collected or assigned.
Note, however, that a project should not be broken down to too
great an extent. If some work packages are too small, unnecessary
administrative effort will be expended in maintaining the information
flow. This suggests some additional rules governing work packages:
Rule 8:On small projects the following "test of reasonableness"
is suggested:æ a work package should at least be large enough to
constitute a scope of work that could be competitively bid and contracted
for by itself.
Rule 9: On large, multi-million dollar projects design work
packages should not be less than, say, 300 man-hours and two months
For construction, a minimum work package value of, say, 0.1 percent
is a good rule of thumb.
A number of work packages may be assembled into a contract
package for procurement purposes. Within such a contract, the identity
of the individual work packages should be maintained for control
purposes. However, to be consistent with the Work Package definition,
the following further rule must be applied:
Rule 10: The same work package must not appear in more than
one contract. If this is likely to happen, the affected work package
should be subdivided, and the respective parts separately defined