Value vs. Cost in Software Sizing and Estimation
Stripped down to the bare bones, value in software estimation measures the functionality that a software product provides to its users (both human and non-human) while production cost measures not just value but the work that is required to deliver that functionality. Software estimates need to account for both. Examples of non-functional cost items include configuration, throw-away code, cloud architecture, and quality requirements. Size measures such as IFPUG and NESMA function points quantify value (delivered functionality) and are recognized as functional size measures. Both measures intentionally ignore technical requirements. They can be very useful when used for asset management, measuring scope creep on a project, or assessing software quality (defect density per delivered unit). For estimating they are an important input; but one that needs to be supplemented to reflect the non-functional cost factors: i.e. what needs to be done behind the scene to create that functionality.