<Li> Purpose <Ul> <Li> Definitions </Li> <Li> Background </Li> <Li> System overview </Li> <Li> References </Li> </Ul> </Li> <Ul> <Li> Definitions </Li> <Li> Background </Li> <Li> System overview </Li> <Li> References </Li> </Ul> <Li> Overall description <Ul> <Li> Product perspective <Ul> <Li> System Interfaces </Li> <Li> User interfaces </Li> <Li> Hardware interfaces </Li> <Li> Software interfaces </Li> <Li> Communication Interfaces </Li> <Li> Memory Constraints </Li> </Ul> </Li> <Li> Design constraints <Ul> <Li> Operations </Li> <Li> Site Adaptation Requirements </Li> </Ul> </Li> <Li> Product functions </Li> <Li> User characteristics </Li> <Li> Constraints, assumptions and dependencies </Li> </Ul> </Li> <Ul> <Li> Product perspective <Ul> <Li> System Interfaces </Li> <Li> User interfaces </Li> <Li> Hardware interfaces </Li> <Li> Software interfaces </Li> <Li> Communication Interfaces </Li> <Li> Memory Constraints </Li> </Ul> </Li> <Li> Design constraints <Ul> <Li> Operations </Li> <Li> Site Adaptation Requirements </Li> </Ul> </Li> <Li> Product functions </Li> <Li> User characteristics </Li> <Li> Constraints, assumptions and dependencies </Li> </Ul>

What are the key elements of software requirements specification (srs)