Software Engineering

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CHAPTER 17 
Software Requirements Definition
The software requirements definition stage occurs one time during the software 
development effort unless an incremental or evolutionary development strategy has 
been chosen. This stage generates the requirements specifications against which 
the computing environment and software product will be developed. The software 
requirements analysis practice will be conducted throughout the software engineer-
ing effort to resolve challenges or risks associated with the software product or 
post-development process requirements.
During this stage of development the focus is to ensure that the requirements 
specified for the software product and post-development processes are complete, 
feasible to achieve within project objectives and constraints, and introduce mini-
mal risks to the project. Functional analysis and allocation should be performed to 
decompose software product requirements and allocate them among the software 
configuration items and elements of the computing environment. At this stage of 
development, the software product physical architecture should identify the soft-
ware configuration items and the elements of the computing environment. This 
results in specifications for the software configuration items, the software external 
interfaces, and the computing environment.
Staffing for the software implementation, computing environment implementa-
tion, post-development, and test and evaluation organizations should be limited to 
the personnel qualified to support the software engineering effort. There are no ben-
efits to be secured by excessively staffing these organizations until the state of the 
software architecture warrants workforce escalation.
The software requirements baseline must be established to control the require-
ments against which the product is to be developed. This is a technical baseline that 
is to be managed by the software engineering integrated product team (SWE-IPT) 
until the formal functional requirements baseline is established. The software require-
ments baseline should not be established until the software architecture has been ver-
ified to be adequately specified, congruent, and amenable to all stakeholders. Once 
the software requirements baseline has been established, the technical change con-
trol board (CCB) must approve changes to this baseline. Once the functional require-
ments baseline is established, the project-level CCB must approve changes to it.
Whenever there is a proposed change to the requirements the SWE-IPT should 
evaluate the impact of the change on the requirements baseline. The software 
requirements analysis tasks should be performed to identify alternative require-
ments assertions that satisfy the proposed change. The software analysis practice 
should be performed to determine the best requirements statement to be specified.