398982625_e475db57c5_bThe fourth step in our checklist for selecting a size metric is an evaluation of the temporal component. This step focuses your evaluation on answering the question, “Is the metric available when you need it?” When do you need to know how big a project is depends on what you intend to do with the data (that goal thing again). The majority of goals can be viewed as either estimation related (forward view) or measurement related (historical view). Different sizing metrics can be initially applied at different times during a project’s life. For example, Use Case Points can’t be developed until Use Cases are developed, lines of code can’t be counted until you are deep into construction, or at the very earliest, in technical design.

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The major dichotomy is between estimation needs and measurement needs. As Figure 4 suggests, determining size from requirements (or earlier) will require focusing on functional metrics. Functional metrics can be applied earlier in the process (regardless of methodology) because they are based on a higher-level of abstraction that is more closely aligned with the business description of the project. Developing estimates or sizing later in the in the development process opens the possibility of more physical metrics which are more closely aligned with how developers view their work.

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