1. Cybernetics and Software Dr K. Dimopoulos CITY College

2. 2 Cybernetics:  Control and Communication in the Animal and the Machine -Norbert Wiener, 1944  [n] The field of science concerned with processes of communication and control (especially the comparison of these processes in biological and artificial systems).

3. 3 Origins  Κυβερνήτης: The steersman of a ship, responsible for controlling the steering wheel and thus affecting the direction of the ship.  Governor: Latin corruption of the Greek word. Also a 19 th century centrifugal mechanism used in mills to control the angular speed of the mill.

4. 4 Cooking in the old days  When more heat was required the baker added more coal or wood to the stove.  The baker had to monitor the fire to keep the temperature constant.  The baker was part of the system: no automation.

5. 5 Modern day cooking  Switch  Heating elements ( resistances)  Thermometer  Thermostat

6. 6 Cybernetic Cycle  Cause – effect in traditional thinking not enough.  Feedback of information.  The effect is used to determine the next cause.  This loop in information allows us to define self-regulating systems, where errors in the system are detected and are corrected by the system.

7. 7 Software Cybernetics  [n] the field of science concerned with processes of communication and control in software systems.

8. 8 Software Test Process  A software P can be in one of the following states:  Test: P is executed until a failure (or more) is detected.  Debug: P is investigated to detect and correct the error(s).  End: The remaining errors are acceptable.  Testing and Debugging take place concurrently.

9. 9 When should we stop?  When the quality of P is good! But how can I tell this?  The Quality depends on:  The reliability of P to be achieved by a target date (deadline)  The number of errors remaining in P

10. 10 Managing the test process  Some Considerations:  Constitution of test team (how many testers to use?)  Experience of each tester  Selection of test tools  LIMITED BUDGET  The manager must decide how much effort is needed.  This is like cooking in the old days.

11. 11 Closed Loop (feedback) Control wf+wfwf+wf  +  wf+wfwf+wf r observed (t) r expected (t) r error (t) Actual STP scsc r0r0 STP Model scsc r0r0 Initial Settings (w f,  ) Controller  ’  w’ f + +  wfwf Test Manager w f : workforce  : quality of the test process

12. 12 Physical and Software Systems: An Analogy Dashpot Rigid surface External force Xequilibrium X: Position Number of remaining errors Spring Force Effective Test Effort BLOCK Software Mass of the block Software complexity Quality of the test process Viscosity Xcurrent Spring To err is Human

13. 13 Physical Systems: Laws of Motion [1] First Law: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Does not (seem to) apply to testing because the number of errors does not change when no external effort is applied to the application.

14. 14 Physical Systems: Laws of Motion [2] Newton’s Second Law: The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. First Postulate: The relationship between the complexity S c of an application, its rate of reduction in the number of remaining errors, and the applied effort E is E=S c. r..

15. 15 Physical Systems: Laws of Motion [3] Third Law: For every action force, there is an equal and opposite reaction force. When an effort is applied to test software, it leads to (mental) fatigue on the tester. Unable to quantify this relationship.

16. 16 Spring = Test force The magnitude of the effective test effort is proportional to the product of the applied work force and the number of remaining errors. The magnitude of the force of a spring is proportional to the product of the spring constant and the change in compression.

17. 17 Dashpot = quality of STP The error reduction resistance is proportional to the error reduction velocity and inversely proportional to the overall quality of the test phase. The force of a dashpot is proportional to the velocity and the dashpot constant.

18. 18 Deriving the model of the STP  Using the first postulate, the sum of all efforts must equal the software complexity times the rate of decrease of errors:  The above equation is directly proportional to a standard control problem that has a known solution.

19. 19 Feedback in STP  Can assist the manager in making decisions regarding  the expansion of or reduction in workforce and  the change in the quality of the test process.  Can provide information about whether the objectives will be met and if not what actions to take.