Modelling Heuristics

http://verraes.net

“How do you approach software modelling problems?”
When a client asked me about my mental process, I didn’t have a proper answer — yet. The question intrigued me. Do you need a propensity for modelling, or is it a learnable skill? I embarked on a mission to find modelling heuristics: the mental tools, that help us look at the problem from different angles; the little tricks to validate a model before we build it; the rules of thumb that lead us to iteratively refine our solutions. In this talk, I share some of the ideas I collected from books, from people I interviewed, and from my own experiences.

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Mathias Verraes is a recovering music composer turned programmer, consultant, blogger, and speaker. He advises companies on how to build enterprise web applications for complex business domains. For some weird reason, he enjoys working on large legacy projects: the kind where there’s half a million lines of spaghetti code, and nobody knows how to get the codebase under control. He’s the founder of the Domain-Driven Design Belgium community. When he’s not working, he’s at home in Kortrijk, Belgium, helping his two sons build crazy Lego train tracks.

Transcript

1. Modelling Heuristics
   @mathiasverraes
   

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2. Mathias
   Verraes
   Independent Consultant
   Value Object Comm.V
   Student of Systems
   Meddler of Models
   Labourer of Legacy
   verraes.net
   

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3. Is modelling a
   learnable skill?
   

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4. The pain of a
   wrong abstraction
   

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5. Upfront Model? 1
   1 Scott W. Ambler, "Big Modeling Up Front (BMUF) Anti-Pattern", http://www.agilemodeling.com/
   essays/bmuf.htm
   

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6. You are always making
   mental models
   

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7. Analysis model 2
   vs
   Domain model
   2 Martin Fowler, 1996, "Analysis Patterns: Reusable Object Models"
   

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8. Heuristic
   Domain
   Language
   

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9. Linguistic
   Relativism
   Sapir-Whorf Hypothesis 3,4
   4 Paul Graham, "Beating the Averages", http://www.paulgraham.com/avg.html
   3 Steven Pinker, 1994, "The Language Instinct"
   

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10. Heuristic
    Find the Nouns
    Anti-pattern?
    

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11. Heuristic
    Descriptive vs Influential
    Properties
    

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12. [ {
    "licensePlate": "1-ABC-123",
    "brand": "BMW",
    "make": "X1",
    "color": "Aggregate Blue",
    ...,
    "location": "40.7127837,-74.0059413"
    },
    ...
    ]
    

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13. Heuristic
    Static / Dynamic
    

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14. Heuristic
    Find the Verbs
    Commands
    

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15. Verb-based:
    f = chain(
    breakTextIntoWords() : [String]
    groupWordsIntoLines() : [[String]]
    joinWordsInBrokenLines() : [String]
    joinBrokenLines() : String
    )
    f("A long paragraph") -> "A long\nparagraph"
    

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16. Noun-based: 7
    f = chain(
    words() : [String]
    brokenLines() : [[String]]
    wordJoinedLines() : [String]
    joinedLines() : String
    )
    f("A long paragraph") -> "A long\nparagraph"
    7 Michael Feathers, "A Type Driven Approach to Functional Design", InfoQ
    

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17. Heuristic
    Find the Sentences
    Find the Idioms
    

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18. Heuristic
    Find the Scenarios
    

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19. Given I have a product
    When I look at the price of a product ...
    or
    Given I have a product
    When I lookup the product in the pricing table ...
    ?
    

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20. Remember, you are always
    making mental models
    

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21. As a customer I want to ...
    Given there is a product
    When I look at the price of a product ...
    As a shop owner I want to ...
    Given I have a product
    When I lookup the product in the pricing table ...
    

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22. Heuristic
    Actors and Roles
    

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23. Heuristic
    The Worker and
    the Beneficiary
    

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24. When I look at the price of a product ...
    When I lookup the product in the pricing table ...
    

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25. Heuristic
    Segregating
    Reading and Writing
    

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26. Heuristic
    Being
    Behaving
    Becoming
    Three B's 5
    5 Gerald M. Weinberg, 1988, "Rethinking Systems Analysis and Design"
    

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27. The customer sometimes has an email.
    Missing concept?
    

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28. Heuristic
    Collaborative Construction6
    Execution
    Tracking
    aka Planning/Execution/Analysis
    6 Cyrille Martraire, "Collaborative Construction by Alberto Brandolini", http://
    cyrille.martraire.com/2012/09/collaborative-construction-by-alberto-brandolini/
    

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29. Heuristic
    Domain Events8
    8 http://verraes.net/2014/11/domain-events/
    

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30. Time ->
    

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31. Heuristic
    Cause &
    Consequence
    

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33. Cause & Consequence
    Human
    External system
    Process
    Time
    

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34. Heuristic
    Business Rules
    Reasons for failure
    

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36. Heuristic
    Consistency
    Boundary
    

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39. Heuristic
    Entity Inclusion
    

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41. Heuristic
    Temporal Expansion
    

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43. Heuristic
    Temporal Shift
    

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45. Heuristic
    Invariant Inclusion
    

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47. Heuristic
    Conceptual Shift
    

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49. Heuristic
    Crossing Streams
    

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51. Heuristic
    Happy Path /
    Divergent Path9
    9 Mathias Verraes, "Event Storming: on Fake Domains and Happy Paths", http://verraes.net/
    2014/07/event-storming-fake-domains-happy-paths/
    

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52. Formal
    Informal
    Aformal
    

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53. Throw Away the Model
    

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54. @mathiasverraes
    verraes.net
    Workshops Domain-Driven Design
    verraes.net/workshops
    Ghent, Belgium, January 20-22
    Newcastle, UK (TBC)
    

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