D.1 The applicability of requirements in this directive to specific systems and subsystems containing software is determined through the use of the NASA-wide software classification structure. These definitions are based on: (1) usage of the software with or within a NASA system, (2) criticality of the system to NASA’s major programs and projects, (3) extent to which humans depend upon the system, (4) developmental and operational complexity, and (5) extent of the Agency’s investment. Classes A through E cover engineering-related software. Class F cover Business and Information Technology Infrastructure Software. Using the Requirements Mapping Matrix, the number of applicable requirements and their associated rigor are scaled back for lower software classes. Situations in which a project contains separate systems and subsystems having different software classes are not uncommon.
