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7150 Requirements Guidance

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7.17 - Work Breakdown Structures That Include Software
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1. Purpose

Topic 7.17 provides guidance on the development of a work breakdown structure (WBS) for software on projects. The WBS provides a common planning framework to use in estimating the scope of a project.

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2. Definition

Per the NASA Systems Engineering Handbook (Section 6.1.2.1) 1, a work breakdown structure is a hierarchical breakdown of the work necessary to complete a project. The WBS can be product or process oriented. A product-oriented WBS has work activities grouped by the product or service they support. A process-oriented WBS has work activities associated with the processes used included in the appropriate WBS element. 3 The WBS provides the framework to plan, organize, and control a
project. 2

Excellent information on the development and usage of the WBS can be found in NASA/SP-2010-3404 NASA Work Breakdown Structure (WBS) Handbook. 4 Additionally, both the NASA Systems Engineering Handbook 1 and the "CMMI for Development, Guidelines for Process Integration and Product Improvement" 2 provide further guidance on the development of WBS structures containing software. The NASA Software Engineering curriculum, especially

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3 , addresses the use of the WBS for software on projects. These resources are cited in the Resources tab of this guidance topic.

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3. The Basic WBS

A project's software may be a stand-alone system or exist as part of a larger system or project. For example, for a space flight project, software may be shown under the Avionics subsystem. For both types, the WBS developer needs to be aware of the responsibilities required of his or her project.

The WBS should be updated iteratively over the project life cycle . The initial WBS is used for early estimating of cost and schedule. The detailed WBS helps organize and control the work done by populating the project's cost plans and schedule.

A companion WBS dictionary should also be developed that fully describes the work being done including the title and objective of the element, expected products/services from each element, and the dependencies between elements.

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4. Common Issues

There are several work activities that are often forgotten in developing the WBS:

  • Process planning and monitoring activities
  • Requirement engineering activities
  • Formal review activities
  • Development activities
  • Stakeholder activities
  • Training activities
  • Planning, documenting, and tracking of commitments from other organizations
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5. Resources

The following are excellent resources for help with developing and using a WBS.

  1. NASA Systems Engineering Handbook, NASA SP-2007-6105, Rev1, NASA Headquarters, 2007.
  2. Chrissis, M.B., et al. (March, 2011). CMMI for Development Guidelines for Process Integration and Product Improvement; Third Edition. SEI Series in Software Engineering. Addison-Wesley Professional.
  3. APPEL Software Engineering Management 301 (SWE 301). Course from APPEL: Academy of Program/Project & Engineering Leadership. Located via the NASA website at http://www.nasa.gov/offices/oce/appel/curriculum/courses/appel_swe-301.html.
  4. NASA SP-2010-3404. "NASA Work Breakdown Structure (WBS) Handbook." NASA Headquarters. January 2010.
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