74 Requirements Engineering for Software and Systems
for every input possibility. Functional requirements may use case-by-case descrip-
tion or other general forms of description (e.g., using universal quantification, use
cases, user stories).
e 830 is not prescriptive in terms of how to organize specific functional
requirements; instead, a menu of organizational options is offered. Specific func-
tional requirements can be organized by
functional mode (e.g., “navigation,” “combat,” “diagnostic”) ◾
user class (e.g., “user,” “supervisor,” “diagnostic”) ◾
object (by defining classes/objects, attributes, functions/methods, and messages) ◾
feature (describes what the system provides to the user) ◾
stimulus (e.g., sensor 1, sensor 2, actuator 1