I used these slides during my talk at the IPA Spring Days in Garderen, The Netherlands (2012).

1. Linguistic diversity in
open-source development
Bogdan Vasilescu
Alexander Serebrenik
Mark van den Brand

2. Motivation
… …
I „speak‟ Java C
C++ …
HTML
Lisp
XML
Java
Python
Unix shell
I „speak‟ Java I „speak‟ Python
and Python
/ Mathematics and Computer Science 23-4-2012 PAGE 1

3. Motivation
If leaves the project, what is the risk of not finding
replacement developers that speak Python?
No risk, plenty of other Python What about now?
developers to choose from
/ Mathematics and Computer Science 23-4-2012 PAGE 2

4. Linguistic diversity
• Greenberg (1956)
• compare geographic regions
• probability that two random individuals do not speak the
same language
/ Mathematics and Computer Science 23-4-2012 PAGE 3

5. Linguistic diversity
Probability that two random individuals do not speak the same language
• Simple model
• everyone speaks exactly one language
• languages are independent
2 S
A 1 p  p
 L P
/ Mathematics and Computer Science 23-4-2012 PAGE 4

6. Linguistic diversity
Probability that two random individuals do not speak the same language
• Related-languages model
• everyone speaks exactly one language
• languages are similar
S
B 1 p pm sim(, m) p
,m L P
0 sim(, m) 1
sim(, ) 1
/ Mathematics and Computer Science 23-4-2012 PAGE 5

7. Linguistic diversity
Probability that two random individuals do not speak the same language
• Polyglot related-languages model
• everyone speaks at least one language
• languages are similar
sim(, m)
 s ,m t Xs
F 1 ps pt ps
s ,t P ( L ) s t P
L A, B, C P ( L) A, B, C , AB, AC , BC , ABC
/ Mathematics and Computer Science 23-4-2012 PAGE 6

8. Our risk measure
• Probability that two random individuals do not speak the
same language
sim(, m)
 s ,m t
F 1 ps pt
s ,t P ( L ) s t
• Risk of not finding developers that „speak‟ 
risk () 1 ps maxk s sim (k )
s P( L)
/ Mathematics and Computer Science 23-4-2012 PAGE 7

9. StackOverflow.com
/ Mathematics and Computer Science 23-4-2012 PAGE 8

10. User tags
/ Mathematics and Computer Science 23-4-2012 PAGE 9

11. Similarity measure
• Reverend Gonzo: Java, C, C++, C#, Python,…
• Alexander Serebrenik: Prolog, SQL, C++,…
• Bogdan Vasilescu: Python,…
• Jon Skeet: C#, Java, ASP.net, XML,…
• … > 400,000
• Association rule mining:
Java
• “C => Java”
nBoth C
sim k conf k 
nLeft
/ Mathematics and Computer Science 23-4-2012 PAGE 10

12. Similarity measure - results
• Assembly posts: 44
• Assembly + Java developers: > 1000
 When in need for Java developers, ask Assembly guys
/ Mathematics and Computer Science 23-4-2012 PAGE 11

13. Case study - Emacs
• 1985-2012: C, Emacs Lisp, C++, Java, Lisp, Python, M4, … (26)
Exotic languages
High/low risk
/ Mathematics and Computer Science 23-4-2012 PAGE 12

14. Case study - Emacs
C: spoken by half of the community
+ similar to other languages Python: spoken very sporadically
low risk + similar to other languages
 low risk
/ Mathematics and Computer Science 23-4-2012 PAGE 13

15. Conclusions
What is the risk of not finding developers
that speak Python?
• Risk measure risk () 1 ps maxk s sim (k )
s P( L)
• Similarity measure (StackOverflow)
• “C => Java” sim k conf k nBoth

nLeft
Low risk Depends on similarity
/ Mathematics and Computer Science 23-4-2012 PAGE 14