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1 CS101 Introduction to Computing Lecture 24 Design Heuristics
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2 During the last lecture … We became familiar with the various phases of the process that developers follow to develop SW systems of reasonable complexity We looked at a couple of problems related to the Waterfall SW development model
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3 In order to understand anything, you must not try to understand everything Aristotle
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4 efficiency 1 universality
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5 focus!
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6 Today’s Lecture Heuristics for System Architecting We will try to understand the role of heuristics in architectural (or high-level) design We will become familiar with a few popular design heuristics
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7 Heuristic?
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8 Heuristic Rule of thumb learned through trial & error Common sense lesson drawn from experience Qualitative principle, guideline, general judgement Natural language description of experience
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9 ? Heuristic Wisdom
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10 Caution ! Caution ! Caution ! Caution ! Heuristics don’t always lead to the best results At times they even lead to the wrong ones, but mostly to results that are good-enough
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11 system?
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12 System A collection of elements which working together produces a result not achieved by the things alone
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13 System Architecture?
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14 System Architecture The structure (in terms of components, connections, constraints) of a product or a process
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15 Design == Architecture ?
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16 Heuristics for system architecting Rules and lessons learnt by system architects after long experiences which when followed result in sound, stable, practical systems
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17 My favorite system architecting (and other relevant) heuristics --- in no particular order ---
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19 1st Given many parts of a system to be designed/built, do the hard part 1st
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20 # 3 All the serious mistakes are made on the very first day
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21 # 4 Simplify, simplify, simplify ! Probably the most useful heuristics for increasing reliability while decreasing cost & time-to-build
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22 Caution ! Caution ! Everything should be as simple as possible but not simpler Al Einstein
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23 # 5 If you can’t explain it in 5 minutes, either you don’t understand it or it does not work
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24 # 6 A system will develop & evolve much more rapidly if there are stable intermediate forms than if there are not Build iteratively; add features gradually
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25 # 7 Success is defined by the user, not the builder
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26 Customer is always right ?
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27 It depends ! # 8 It’s more important to know what the customer needs instead of what he says he wants
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28 # 9 If you think that your design is perfect, it is only because you have not shown to anyone else --- Get your designs reviewed ---
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29 # 10 A good solution to a problem somehow looks nice & elegant
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30 #11 In partitioning, choose the chunks so that they are as independent as possible Chunks should have low external complexity & high internal complexity Organize personal tasks to minimize the time individuals face interfacing
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31 2 6 5 4 31
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32 2 6 5 4 31
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33 2 6 5 4 31
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34 1 2 3 5 6 7 8 4 9
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35 #12 Partition/repartition the problem until a model consisting of 7±2 chunks emerges
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36 Life is the art of drawing sufficient conclusions from insufficient premises Samuel Butler
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37 #13 When choices must be made with unavoidably inadequate info: Choose the best available & then watch to see: whether further solutions appear faster than future problems If so, the choice was at least adequate If not, go back & choose again
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38 #14 The Triage 1. Let the dying die 2. Ignore who’ll recover on their own 3. Treat only those who’ll die without your help
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39 # 15 Don’t just remove the defect;...
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40 # 15 Don’t just remove the defect; correct the process that caused it
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41 #16 The number of defects remaining in a system after a given level of tests is proportional to...
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42 #16 The number of defects remaining in a system after a given level of tests is proportional to the number found during the test
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43 #17 Programmers deliver the same number of LOC/day regardless of the language they are writing in Use the highest-level language
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44 There are many more! Please post any that are familiar to you on the message board
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45 In Today’s Lecture We became familiar with the the role of heuristics in design We also discussed a few well-known design heuristics for architectural design
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46 Next Lecture: Web Design for Usability To become able to appreciate the role of usability in Web design To become able to identify some of the factors affecting the usability of a Web page
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