Getting started with DRAKON flowcharts

1. DRAKON Visual
Language
Tutorial. Part 1:
How to draw DRAKON flowcharts

2. Types of DRAKON diagrams
Primitive
Silhouette
Used for the most simple
algorithms
Recommended for all
other algorithms

3. Primitive

4. What does a primitive consist of?

5. What does a primitive consist of?
A vertical skewer

6. What does a primitive consist of?
The header

7. What does a primitive consist of?
The algorithm

8. What does a primitive consist of?
The “End” icon

9. “Action” icon
An “Action” icon

10. “Action” icon
an order to do
something

11. The skewer must be vertical

12. Wrong!

13. Wrong again
●
Use lines instead of arrows
●
Arrows create visual noise
In DRAKON,
the next icon is always below

14. Even worse
●
It is not allowed to break the skewer

15. “Insertion” icon
It is a reference
to an algorithm
that is defined elsewhere

16. “Insertion” icon

17. “If” icon

18. “If” icon
Contains a question
that can be answered
“yes” or “no”

19. The happy path goes straight
The happy path
is the most successful
and desirable route

20. The unlucky scenario goes to the right

21. The further to the right,
the worse it is

22. Good
Bad
Worst

23. Wrong
The happy path
is broken

24. Right
The happy path
is straight

25. Visual noise is bad
Too many angles

26. Horizontal joining
The problem is solved

27. Repetition is bad

28. Vertical joining
Removes repetition

29. Line intersections
are forbidden

30. Intersections kill readability

31. Silhouette
The recommended type of diagrams

32. What can silhouette do?
●
It can cleanly split the diagram into logical
parts
●
It can represent a finite automaton (state
machine)
●
It helps get rid of line intersections in complex
algorithms

33. What does a silhouette consist of?

34. The header

35. The branches

36. What does a branch consist of?
A header with
the branch name

37. What does a branch consist of?
The algorithm
of the branch

38. What does a branch consist of?
The address
of the next branch

39. Silhouette answers
the three questions of the king:
1. What is the name of the problem?
2. How many parts does the problem have?
3. What are the names of the parts?

40. 1. What is the name of the problem?

41. 2. How many problems does the problem have?

42. 3. What are the names of the parts?

43. The leftmost branch is run first

44. Then follow the other branches

45. The rightmost branch goes last

46. There can be only one
“End” icon
on the DRAKON diagram

47. The order of branches is defined in the “Address” icons

48. The branches should by sorted left-to-right

49. When is it allowed to go to the left?
1. When some branches need to be repeated.
2. When the diagram represents a finite
automaton (state machine).

50. A branch can have several “Address” icons
The algorithm of such branch
decides which branch to run next

51. A direct jump from one branch to another is
forbidden

52. Icon “Select”
Contains a question:
●
that cannot be answered “yes” or “no”
●
that can have several answers

53. Icon “Select”

54. How to arrange the answers?
●
Following the principle “The further to the right, the
worse it is”
or
●
Following the principle “The further to the right, the
larger it is”
or
●
Following the principle “The further to the right, the
higher it is”
or...
The key thing is to sort the answers

55. The further to the right, the larger it is

56. Loops

57. Lift the weight while not tired

58. The body of this loop
is run at least once

59. Hungry?
If yes, then
eat a hamburger
start from the
beginning
If no, then leave

60. This loop is skipped if the condition is not met

61. The loop condition is inside the loop body

62. “For each” loop

63. There can be several exits from a loop

64. There can be only ONE ENTRANCE
into a loop
Wrong!
A second
entrance is
not allowed

65. Silhouette loop: some branches are run several times

66. Silhouette loop: some branches are run several times
Loop branches are marked
with black triangles

67. “Select” loop

68. Stepan Mitkin
stipan.mitkin@gmail.com
The diagrams on the slides were made with
DRAKON Editor
http://drakon-editor.sourceforge.net/
June 2013
End