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Lecture 2: Software Life cycle

Lecture 2: Software Life cycle. Lazy. Contemplative. Always Using Imagination. Most Important Trait. Why Do Models Matter?. Client has 2 programmers with different styles. Bob. Joe. More about Bob & Joe…. Bob codes like Joe paid attention & like he did in college uses a proper model.

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Lecture 2: Software Life cycle

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  1. Lecture 2:Software Life cycle

  2. Lazy

  3. Contemplative

  4. Always Using Imagination

  5. Most Important Trait

  6. Why Do Models Matter? • Client has 2 programmers with different styles Bob Joe

  7. More about Bob & Joe… Bob codes likeJoe paid attention & like he did in collegeuses a proper model

  8. Starting the Project • Both look at notes from project executive • Bob then writes test cases & starts coding • Joe determines client’s needs in meetings

  9. Project Getting Going • Bob duplicates code, but with minor tweaks • Slows progress & requires expensive reworking • Design minimizing code created by Joe • Client’s requirements examined; bugs found & fixed

  10. Passing the Halfway Point • Bob works from scratch & does not reuse code • Lacks plan to incorporate existing code • Joe uses design to write comments & outlines • Finds majority of errors during this process • When possible, merges classes & simplifies design

  11. Project Nearing Completion • Bob’s code is project-specific& cannot be reused • Getting concerned as project starts falling behind • Joe writes test cases from his system design

  12. Final Rush to the Deadline • Bob cannot describe system to get extra help • Completing system takes lots of all-nighters • Joe’s coding is easy with well-defined tests • Code could be written by (cheap) trained monkeys Bob Joe

  13. Final Rush to the Deadline • Bob cannot describe system to get extra help • Completing system takes lots of all-nighters • Joe’s coding is easy with well-defined tests • Code could be written by (cheap) trained monkeys Bob Joe Joe’s Team

  14. Final Accounting

  15. What’s The End Result? • Bob barely finishes • Most goalsare met • Occasionally crashes • Close to original goal • Joe is tanned & rested • Met stated goals • Reliable & robust • Follows design perfectly

  16. What’s The End Result? • Client fires them both • Neither met requirements • Bob barely finishes • Most goals are met • Occasionally crashes • Close to original goal • Joe is tanned & rested • Meets all needs • Reliable & robust • Exactly follows design

  17. Models Matter • Client valued original concept above all else • Joe and Bob both forgot about this main point • Joe gets better chair in unemployment line • To survive, life cycle models must succeed • Nobody records failures or the merely adequate • But common saying is “There is no silver bullet” • One shared weakness no matter your choices • Need to keep your focus on requirements • Keep in mind when being lazy

  18. Classroom Development • Always start from scratch • Know all requirements from the start • And requirements will not change • Coding begins immediately at start • Projects are trivial jokes in real-world • If lasts 3 weeks, projects “very large” • Code cannot be reused • Never look at again, anyway

  19. Why These Phases Matter

  20. Waterfall Model • Shows steps project goes through • Can compress, but steps never skipped • Assumes steps not revisited once done • Each step ends with some result • Evidence process followed correctly • Begin by testing results of previous

  21. Moving Target Problem • During development, requirements may change • Changes may be important, but… • …disrupts flow & introduces dependencies • Regression faults occur without good testing • Error (“fault”) usually in unrelated portion of project • Major pain to fix • As changes continue, faults will build up • Redesign & reimplementation ultimately needed • Change is inevitable • Your plans must handle gracefully

  22. Waterfall Model Is Iterative Waterfall Model Is Iterative

  23. Waterfall Model Is Iterative Waterfall Model Is Iterative Heck of a job, Brownie.

  24. Incremental Development • Waterfall improved by working incrementally • Focus on most important piece at the moment • Follow waterfall model to develop that piece • Focus on new most important piece once complete • Method also called stepwise refinement • Best of both worlds is incremental methods goal • Amount of duplicative work minimized • Improved reaction to change using smaller chunks • But handling changes requires good design & plans

  25. For Next Lecture • Reading for Mondayavailable on Angel • Will be discussing software requirements • What are they? • How do we figure them out? • Can they be discussed in our teams? • Weekly activity problem #2 due at start of class • Discussed at start of lecture, just like today • Available on weekly assignment page

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