A mental model is an explanation of how something works. It is a concept, a framework or a vision of the world that you carry in your mind to help you interpret what surrounds you and understand the relationship between things. This talk explores how software projects are very complex systems that we should approach from different mental models, applying multidisciplinary thinking. Pamplona Software Crafters 2018 #scpna http://pamplonaswcraft.com/

1. Mental models,
complexity and software
Arturo Herrero

4. • MyDrive 2016 Telematics
• Mastered 2015 Fashion courses
• Coinfloor 2014 Bitcoin exchange
• Cambridge Healthcare 2013 Medical management
• OSOCO 2010 Software development

5. Skin in the game

6. Que sais-je?
(What do I know?)

7. Complexity

8. • Big O notation
• Cyclomatic Complexity
• The ABC Metric
• Ruby’s Flog Score
• Cognitive Complexity

15. Chaos is order yet undeciphered

17. 1614: The white king commands his owne knight
into the third house before his owne bishop.
1750: K. knight to His Bishop's 3d.
1837: K.Kt. to B.third sq.
1848: K.Kt. to B's 3rd.
1859: K. Kt. to B. 3d.
1874: K Kt to B3
1889: KKt-B3
1904: Kt-KB3
1946: N-KB3
Modern: Nf3

20. You can always recognize truth by its
beauty and simplicity.
– Richard Feynman

21. User.create(name: "Arturo")

22. {
• Coerce attributes
• Validate attributes
• Database validations
• Trigger callbacks
• Handle associated data
• Invoke overridden behaviours
• Autosave
• Touching
• Counter updates

24. /*------------------------------------------------------------
HELLOWIN.C -- Displays "Hello, Windows 95!" in client area
(c) Charles Petzold, 1996
------------------------------------------------------------*/
#include <windows.h>
LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static char szAppName[] = "HelloWin" ;
HWND hwnd ;
MSG msg ;
WNDCLASSEX wndclass ;
wndclass.cbSize = sizeof (wndclass) ;
wndclass.style = CS_HREDRAW | CS_VREDRAW ;
wndclass.lpfnWndProc = WndProc ;
wndclass.cbClsExtra = 0 ;
wndclass.cbWndExtra = 0 ;
wndclass.hInstance = hInstance ;
wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ;
wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;
wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
wndclass.lpszMenuName = NULL ;
wndclass.lpszClassName = szAppName ;
wndclass.hIconSm = LoadIcon (NULL, IDI_APPLICATION) ;
RegisterClassEx (&wndclass) ;

25. hwnd = CreateWindow (szAppName, // window class name
"The Hello Program", // window caption
WS_OVERLAPPEDWINDOW, // window style
CW_USEDEFAULT, // initial x position
CW_USEDEFAULT, // initial y position
CW_USEDEFAULT, // initial x size
CW_USEDEFAULT, // initial y size
NULL, // parent window handle
NULL, // window menu handle
hInstance, // program instance handle
NULL) ; // creation parameters
ShowWindow (hwnd, iCmdShow) ;
UpdateWindow (hwnd) ;
while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg) ;
DispatchMessage (&msg) ;
}
return msg.wParam ;
}
LRESULT CALLBACK WndProc (HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc ;
PAINTSTRUCT ps ;
RECT rect ;
switch (iMsg)
{

26. case WM_CREATE :
PlaySound ("hellowin.wav", NULL, SND_FILENAME | SND_ASYNC) ;
return 0 ;
case WM_PAINT :
hdc = BeginPaint (hwnd, &ps) ;
GetClientRect (hwnd, &rect) ;
DrawText (hdc, "Hello, Windows 95!", -1, &rect,
DT_SINGLELINE | DT_CENTER | DT_VCENTER) ;
EndPaint (hwnd, &ps) ;
return 0 ;
case WM_DESTROY :
PostQuitMessage (0) ;
return 0 ;
}
return DefWindowProc (hwnd, iMsg, wParam, lParam) ;
}

27. Most software today is very much like an Egyptian pyramid with
millions of bricks piled on top of each other, with no structural
integrity, but just done by brute force and thousands of slaves.
– Alan Kay, Dec 2004

28. Complexity is not free
Increases the hidden risks and the fragility
of the system.

29. • Style guides
• Tests
• Refactoring. KISS. YAGNI
• Domain Driven Design
• Automation. DevOps. CI/CD
• Rollback strategies
• Data Redundancy
• Chaos Engineering
• Post-mortems
• Kaizen. Iterations. Retros

31. Always understand one level below your
normal abstraction layer.
– Neal Ford

32. Always understand one level above your
normal abstraction layer.
– Arturo Herrero

33. Mental models

35. It is remarkable how much long-term advantage
people like us have gotten by trying to be consistently
not stupid, instead of trying to be very intelligent.
– Charlie Munger
I’m not a great programmer;
I’m just a good programmer with great habits.
– Kent Beck

38. Multiple Mental Models
A collection of big ideas from big disciplines
contains a checklist for decision-making.

39. 80/20

40. Minimum Viable Product

41. Confirmation Bias

42. Opportunity Cost

43. Margin of Safety

45. • See the world more accurately and make
better predictions of the future.
• Have more innovative ideas.
• Build more and better connections with
people who are different.

46. • Increase (self-)awareness.
• Ways to work more collaboratively by
understanding your coworkers.
• Ways to improve yourself so you can be
more effective.

47. Summary

48. 1. The world/reality is complex
2. Driven by compression progress
3. Complexity is not free
4. Mental models

50. Remember, always, that everything you know, and everything
everyone knows, is only a model. Get your model out there where
it can be viewed. Invite others to challenge your assumptions and
add their own.
– Donella H. Meadows

51. ¡Gracias!
Arturo Herrero
Mental models,
complexity and software