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SE: System Requirements

Page history last edited by barbara gibson 14 years, 12 months ago

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System Requirements Step Description

In this step the stakeholder needs identified in the Concept of Operations are reviewed, analyzed, and transformed into verifiable requirements for the system. Working closely with stakeholders, the requirements are then further refined to provide the basis for designing the system and for verifying the system once it has been developed and integrated.

Requirements define what the system must do, how well it must perform its functions, and under what conditions it must operate.

Purpose

The purpose of this key step in the systems engineering process is to develop a validated set of system requirements that meet the stakeholder’s needs. The reason that requirements are so important to the system engineering process is that they are used to define the capabilities of the system design and are used to verify that the system in fact possesses all the capabilities (i.e. that the system built meets the requirements).

Activities

The following key activities are performed to develop the system requirements:

Elicit requirements. The first key step is to define an initial set of requirements. Building on the stakeholder needs and other input such as the functional requirements from the regional ITS architecture, and any relevant statutes, regulations, or policies, define a strawman set of system requirements and review and expand on these requirements, working closely with the project stakeholders.

Analyze requirements. This is where the requirements are cleaned up – conflicts are resolved, gaps are identified and addressed, ambiguity and redundancy are removed, and the requirements are organized and decomposed into more detailed requirements. There are a set of “rules” for creating good requirements in the references below.
Document requirements. As will the other steps in the systems engineering process, it is important to document the results of this step. The requirements document will form the basis not only for the design to follow, but also for the verification step that occurs later in the process. To support this later verification step, the documentation of requirements.

Validate requirements- The documented requirements are carefully checked for consistency, accuracy, and completeness. The requirements are also traced to the needs defined in the earlier step. This is a critical activity that is intended to identify requirements defects as early in the process as possible when correcting defects is most economical. To support validation, requirements walkthroughs are held to review the requirements in a systematic way with the project stakeholders and project team.
Manage requirements- Because requirements form the basis for design and for verification, it is very important to manage them throughout the development process. There are a variety of industry tools that can be used to manage the requirements, track changes to the requirements, and provide facilities that support traceability, requirements retrieval and reporting, etc.

Related Resources

Chapter 4.4 System Requirements Systems Engineering for Intelligent Transportation Systems, January 2007

http://ops.fhwa.dot.gov/publications/seitsguide/section4.htm#s4.4

Cost: Free

System / Subsystem Requirements Specification – Appendix G, Florida's Statewide Systems Engineering Management Plan, Version 2, Florida Department of Transporation, March 2005

http://www.floridaits.com/SEMP/Files/PDF_Report/ApxG.pdf

Cost: Free

Requirements Development:[System and Sub-system Level Requirements

Systems Engineering Guidebook for ITS, California Department of Transportation Division of Research and Innovation, January 2007

http://www.fhwa.dot.gov/cadiv/segb/views/document/Sections/Section3/3_5_1.htm

Cost: Free

Chapter 6: Requirements Analysis Phase - Systems Development Life Cycle Guidance Document, Department of Justice, January 2003

http://www.usdoj.gov/jmd/irm/lifecycle/ch6.htm

Cost: Free

IEEE Guide for Developing System Requirements Specifications, IEEE Std 1233, 1998 edition

Cost: (price may range from $61 - $101 depending on retail source)

Buede D. M., The Engineering Design of Systems: Models and Methods, Wiley Inter-Science, 2000

Cost: (price may range from $54 - $110 depending on retail source)

Hooks, I. F., Writing Good Requirements, Paper written for the Third INCOSE Symposium and Published in the Proceedings of the Third International Symposium of the INCOSE - Volume 2, 1993

http://www.complianceautomation.com/papers/writingreqs.htm

Cost: Free

Young, R. R., Effective Requirements Practices, Addison-Wesley, March 2001

http://www.ralphyoung.net/

Cost: (price may range from $30 - $45 depending on retail source)

Sommerville, I., and Sawyer, P., Requirements Engineering, A Good Practice Guide, Chichester: Wiley & Sons, 1997

Cost: (price may range from $57 - $80 depending on retail source)

Note: Much of the material on this page was extracted from http://www.itslessons.its.dot.gov/its/benecost.nsf/LessonSystemsEng.