Step Four: Software Sizing
Size is generally the most significant (but certainly not the only) cost and schedule driver. Overall scope of a software project is defined by identifying not only the amount of new software that must be developed, but also must include the amount of preexisting, COTS, and other software that will be integrated into the new system. In addition to estimating product size, you will need to estimate any rework that will be required to develop the product, which will generally be expressed as source lines of code (SLOC) or function points, although there are other possible units of measure. To help establish the overall uncertainty, the size estimate should be expressed as a least-likely-most range.
Predicting Size
Whenever possible, start the process of size estimation using formal descriptions of the requirements such as the customer’s request for proposal or a software requirements specification. You should reestimate the project as soon as more scope information is determined. The most widely used methods of estimating product size are:
Step One: Establish Estimate Scope and Purpose
Establish Estimate Scope and Purpose
Define and document expectations. When all participants understand the scope and purpose of the estimate, you’ll not only have a baseline against which to gauge the effect of future changes; you’ll also head off misunderstandings among the project group and clear up contradictory assumptions about what is expected.
Documenting the application specifications, including technical details, external dependencies and business requirements, will provide valuable input for estimating the resources required to complete the project. The more detailed the specs, the better. Only when these requirements are known and understood can you establish realistic development costs.
An estimate should be considered a living document; as data changes or new information becomes available, it must be documented and factored into the estimate in order to maintain the project’s integrity.
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Ten-Step Project Estimation Process Introduction
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Step Two: Establish Technical Baseline, Ground Rules, and Assumptions
