1. 1 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Timing Constraints

2. 2 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Timing Constraints Define response time requirements for software and/or the environment Many simple cases –key press response time < 10 msec Four basic types of timing constraints –stimulus-response –response-response –stimulus-stimulus –response-stimulus

3. 3 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Timing Constraints Stimulus is an action performed by the user or environment on the system Response is an action by the system on the user or environment

4. 4 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Stimulus-Response Stimulus-response; constraint that the system must produce a response in accordance with a specified timing relationship to an earlier user stimulus to the system

5. 5 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Stimulus-Response Examples –“The system shall generate a dial tone within 15 seconds of a user taking the phone off the hook” (maximum constraint) –“The system shall arm the door no sooner than 1 minute after the “alarm on” button is pressed” (minimum constraint) Stimulus and response do not need to be adjacent in time

6. 6 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Response-Response Response-response; used to specify a temporal relationship that must exist between two arbitrary system responses in the environment Examples –“The system shall initiate the door closing operation within 20 seconds of locking the landing gear in the retracted state” (maximum)

7. 7 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Response-Response Examples –“The system shall generate a “launch missile” command no sooner than 5 seconds after generating a “start battery warm up” command” (minimum)

8. 8 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Stimulus-Stimulus Stimulus-stimulus; enables us to specify expected behavior of a user or environment of a system in terms of maximum or minimum timing constraints between two stimuli Examples –“Users must type their password within 15 seconds of typing their identification or they will be denied access to the database” (maximum)

9. 9 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Stimulus-Stimulus Examples –“Pilots must not press the “launch weapon” button sooner than 10 seconds after pressing the “fire ready” button” (minimum)

10. 10 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Response-Stimulus Response-stimulus; enables us to specify a temporal relationship that must exist between a system response and a subsequent user stimulus Examples –“The user must dial the complete phone number within 1 minute of hearing the dial tone” (maximum)

11. 11 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Response-Stimulus Examples –“The user may not make a menu selection sooner than 5 seconds after completion of the menu display” (minimum)

12. 12 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering System vs user ?? S-R and R-R define timing requirements on the system being specified Function must be implemented in such a way as to be fast enough (or slow enough) to meet the timing requirement

13. 13 Version 1.0 02/05/2004 © 2004 Robert Oshana Requirements Engineering Timing Constraints S-S and R-S constraints imply the system must be able to detect a violation of timing constraints by the user or environment Do not imply the software must be rapid or slow but there must be additional software –detect inappropriate timed user stimuli –generate alternative response to the user —warning —error message