2. 1.1/46 Scope Of Software Engineering

3. 1.2/46 Prologue… ‘Have you any idea what happened to our computers! Pay $0.00 bill, …, Pay the $0.00 bill within 30 days…, …, Pay the $0.00 bill or possible legal action …, Paying the $0.00 bill,

4. 1.3/46 Prologue - (Cont’d)… On Nov, 11, 1979 the US Worldwide Military Command and Control System (WWMCCS) computer network reported that the Soviet Union has launched missiles aimed towards the US…,WWMCCS Actually, a simulated attack was interpreted as the real thing!,

5. 1.4/46 Prologue - (Cont’d)… 30% of software development projects fail, 70% of the remainder –Are over budget by 189% –Behind schedule by 222%, More than 50% of this trouble is caused by inadequate requirements definition, 352 companies, 8000 Projects. Source: The Standish Group, 1995

6. 1.5/46 Prologue - (Cont’d)… Why SW Projects Fail?

7. 1.6/46 Prologue - (Cont’d) … SW engineering is a discipline whose aim is the production of fault-free software, delivered on time and within budget, that satisfies the users’ needs, Furthermore, the SW must be easy to modify when the users’ needs change.

8. 1.7/46 discipline Discipline – training; punishment; method, system, Self discipline - ability to apply oneself to complete a task or Self discipline is the ability to do what needs to be done, at the time it needs to be done, whether you like doing it or not.

9. 1.8/46 Overview Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

10. 1.9/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

11. 1.10/46 Historical Aspects … 1968 NATO Conference, Garmisch, Germany, Aim: to solve the “Software Crisis”, Software is delivered: –Late, –Over budget, –With residual (שרידי, משקעי ) faults.

12. 1.11/46 Historical Aspects (Cont’d) … Few actual questions: What really happened on 1/1/2000 0:0?, Why was windows 2000 so late? (And why, on its release day, some 64,000 bugs were announced?), How did NASA lose MARS?MARS

13. 1.12/46 Historical Aspects (Cont'd) … Why cannot bridge-building techniques be used to build operating systems?, Compare: Attitude to collapse, Accumulated experience, Complexity, Maintenance (can you please rotate in 90°?).

14. 1.13/46 Historical Aspects - Conclusions Software engineering is not “engineering”, No silver bullet [brooks 1987], What silver bullets are used for?

15. 1.14/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

16. 1.15/46 Economic Aspects Coding method CM new is 10% faster than currently used method CM old. Should it be used?, Common sense answer: “of course!”, Software engineering answer: Cost of introducing CM new to the organization, Cost of shifting to CM new : training, (and not working, learning curve), Consider the effect of CM new on maintenance, Consider the client response.

17. 1.16/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

18. 1.17/46 Maintenance Aspects Software life cycle, The way we produce software, including: The life-cycle model, The individuals, CASE tools.

19. 1.18/46 Life-cycle Model 1.Requirements phase – דרישות, 2.Specification ( & Planning) phase – אפיון, 3.Design phase – תיכון, 4.Implementation phase – יישום, מימוש, 5.Integration phase – שילוב, 6.Maintenance phase – תחזוקה, 7.Retirement – פרישה. System Analysis,

20. 1.19/46 Relative Cost of Each Phase 1976–1981 data, Maintenance constitutes 67% of total cost:

21. 1.20/46 Relative Cost of Each Phase דרישות %2 אפיון %5 תכן %6 קידוד ובדיקות %12 שילוב %8 אחזקה %67 דרישות 2% אפיון 5% תכן 6%

22. 1.21/46 Comparative Relative Cost of Each Phase

23. 1.22/46 Good and Bad Software Good software is maintained — bad software is discarded, Effect of CM new on maintenance.

24. 1.23/46 Different Types of Maintenance Corrective maintenance [about 20%], Enhancement: — תחזוקת הגברה, שיפור, חיזוק Perfective maintenance [about 60%] — תחזוקת השלמה, e.g.: additional functionality or decreased response time, Adaptive maintenance [about 20%] — התאמה תחזוקת. (Responding to an ever-changing environment).

25. 1.24/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

26. 1.25/46 Specification VS. Maintenance Faults 60 to 70 percent of faults are specification and design faults, Data of Kelly, Sherif, and hops [1992]: –1.9 faults per page of specification, –0.9 faults per page of design, –0.3 faults per page of code,

27. 1.26/46 Cost to Detect and Correct a Fault

28. 1.27/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

29. 1.28/46 Team Programming Aspects SW products might be huge: –We can build products that are too large to be written by one person in the available time, Teams: –Interface problems, –Meetings, Communication is cheap: –International teams, –Different working hours, –Cultural differences.

30. 1.29/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

31. 1.30/46 The Object-oriented Paradigm … The structured paradigm had great successes initially –It started to fail with larger products (> 50,000 LOC), Maintenance problems (today, up to 80% of effort), Reason: structured methods are –Action oriented (finite state machines, data flow diagrams); or –Data oriented (entity-relationship diagrams), –But not both.

32. 1.31/46 The Object-oriented Paradigm (Cont'd) Both data and actions are of equal importance, Object: –Software component that incorporates both data and the actions that are performed on that data, Example: –Bank account data:account balance actions: deposit, withdraw, determine balance.

33. 1.32/46 Structured VS. Object-oriented Paradigm Information hiding, Responsibility-driven design, Impact on maintenance, development.

34. 1.33/46 Key Aspects of Object-oriented Solution Conceptual independence: –Encapsulation – כימוס, Physical independence: –Information hiding, Impact on development: –Physical counterpart (מקביל, דומה), Impact on maintenance: –Independence effects.

35. 1.34/46 Responsibility-driven Design Also called “Design by Contract”, Example: Send flowers to your aunt Tel Aviv: –Call 1-800-203040, –Where is 1-800-203040?, –Which Tel-Aviv City florist does the delivery?, –Information hiding, Object-oriented paradigm: –“Send a message by a method [action] of an object“.

36. 1.35/46 Transition From Analysis to Design Structured paradigm: –Jolt ( טלטול) between analysis (what) and design (how), Object-oriented paradigm: –Objects appear from the very beginning.

37. 1.36/46 Analysis / Design “Hump” Systems analysis: –Determine what has to be done, Design: –Determine how to do it, –Architectural design — determine modules, –Detailed design — design each module.

38. 1.37/46 Removing the “Hump” Object-oriented analysis: –Determine what has to be done, –Determine the objects, Object-oriented design: –Determine how to do it, –Design the objects.

39. 1.38/46 In More Detail Objects enter here:

40. 1.39/46 Warning Do not use the object-paradigm to enhance a product developed using the structured paradigm. Water and oil do not mix, Exception: if the new part is totally disjoint –Example: adding a GUI (graphical user interface).

41. 1.40/46 Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

42. 1.41/46 Terminology … Software, program, system, product, Methodology – the science of methods, paradigm – model or pattern, we will use both for: ‘collection of techniques for carrying out the product life-cycle’, Client, developer, user, Cont’d

43. 1.42/46 Terminology (Cont’d) … Bug: –“A bug  crept into the code” Instead of –“I made a mistake”, Whose responsibility is it?

44. 1.43/46 Object-oriented Terminology … Data component of an object: –State variable, –Instance variable (java), –Field (C++), –Attribute (generic), Action component of an object: –Member function (C++), –Method (generic).

45. 1.44/46 Object-oriented Terminology (Cont’d) C++: A member is either: –An attribute (“field”), or, –A method (“member function”), Java: A field is either: –An attribute (“instance variable”), or a –Method.

46. 1.45/46 Summary Historical aspects, Economic aspects, Maintenance aspects, Specification and design aspects, Team programming aspects, The object-oriented paradigm, Terminology.

47. 1.46/46 Scope Of Software Engineering The End