Work breakdown structure (WBS) is a technique to decompose the project for the purpose of management and control. A project may be divided into subprojects. Subprojects are then subdivided into smaller, more manageable work components (work packages) at the lowest level. The work packages may be further decomposed to project activities.
Decomposition involves the major steps as follows[2]:
(1) Identify major elements of the project. In general, the major elements will be project deliverables and project management.
(2) Decide if adequate cost and duration estimates can be developed at this level of detail for each deliverable.
(3) Identify constituent components of the deliverable. Constituent components should be described in terms of tangible, verifiable results to facilitate performance measurement.
(4) Verify the correctness of the decomposition: are the low-level items both necessary and sufficient for completion of the decomposed item? Is each item clearly and completely defined? Can each item be appropriately scheduled and budged?
A WBS provides a description of project deliverables and elements. It should also provide a complete framework for the integrated project scheduling and control.
Work packages are specific, determinable, and deliverable work elements to define and describe work contents, objectives, results, persons in charge, dates, durations, resources and costs.
The deliverables in the WBS are products or services. They should be compatible with the product items in the PBS.
The WBS is the basis for development of organization breakdown structure (OBS) and cost breakdown structure (CBS). It underlies the development of project network schedule and earned value analysis as well.
Product Breakdown Structure
A Product breakdown structure (PBS) is a hierarchy where the project is decomposed into product-oriented components when defining project scope. It defines and describes project deliverable products and product constituent components.
Relationships among WBS, PBS and CBS
The combination of WBS, OBS and CBS provides the structures for cost estimating, constructing the cost control cube.
Configuration Management
Configuration is used to define the functions of project results and their inherent natures. Configuration is described in the documents and tracked in the project process.
Configuration management involves all the technical and organizational measurements, including configuration identification, documentation, recording and auditing. The emphasis is on project deliverables, recording actual configuration status punctually, and controlling any changes.
The change management in the configuration management focuses on controlling the configuration status of the overall project, including project configuration and the definition, description, classification, evaluation, examination, realization and verification of the its attribute change.
Expert Judgment
Expert judgment is often applied to project management. Such expertise may be provided by any group or individual with specialized knowledge or training.
Scope Change Control System
A scope change control system defines the procedures by which the project scope may be changed. It includes documentation, tracking systems, and approval levels necessary for authorizing changes. The scope change control system should be integrated with the integrated change control system. When the project is performed under contract, the scope change control system must also comply with all relevant contractual terms and conditions.