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. -- 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.

1. Modelling Heuristics
@mathiasverraes

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

3. Is modelling a
learnable skill?

4. The pain of a
wrong abstraction

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

6. You are always making
mental models

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

8. Heuristic
Domain
Language

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

10. Heuristic
Find the Nouns
Anti-pattern?

11. Heuristic
Descriptive vs Influential
Properties

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

13. Heuristic
Static / Dynamic

14. Heuristic
Find the Verbs
Commands

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

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

17. Heuristic
Find the Sentences
Find the Idioms

18. Heuristic
Find the Scenarios

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 ...
?

20. Remember, you are always
making mental models

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 ...

22. Heuristic
Actors and Roles

23. Heuristic
The Worker and
the Beneficiary

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

25. Heuristic
Segregating
Reading and Writing

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

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

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/

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

30. Time ->

31. Heuristic
Cause &
Consequence

33. Cause & Consequence
Human
External system
Process
Time

34. Heuristic
Business Rules
Reasons for failure

36. Heuristic
Consistency
Boundary

39. Heuristic
Entity Inclusion

41. Heuristic
Temporal Expansion

43. Heuristic
Temporal Shift

45. Heuristic
Invariant Inclusion

47. Heuristic
Conceptual Shift

49. Heuristic
Crossing Streams

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/

52. Formal
Informal
Aformal

53. Throw Away the Model

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