1. Using IR Methods
for Labeling Source Code Artifacts:
is it Worthwhile?
Andrea
De Lucia
Massimiliano
Di Penta
Rocco
Oliveto
Annibale
Panichella
Sebastiano
Panichella

2. Context
• Source code is text too!
• Lexicon quality impacts software quality
• IR techniques used to analyze software
• Emerging application: label software artifacts
• Labeling packages [Kuhn et al., 2007]
• Labeling changes [Thomas et al., 2010]
• Relate topics in high-level artifacts an source
code [Gethers et al., 2011]

3. ok... but...

4. Are these automatic
labelings meaningful?

5. Related study: Haiduc et al., 2010

6. Empirical Study
Goal: compare human-generated source
code labeling with automatically generated
ones
Quality focus: quality of automatically
generated source code labelings
Perspective: researchers interested to
develop source code labeling techniques

7. Research Questions
RQ1: How much is the overlap between the
keywords identified by developers when
describing a source code artifact and those
identified by an automatic technique?
RQ2:Which are the characteristics of source
code artifacts that affect the overlap of
automatic labeling techniques with the
human-generated labels?

8. Context
Objects:
10 classes from eXVantage (industrial test data
generation tool)
10 classes from JHotDraw
Subjects:
17 software engineering students (Bachelor degree
in CS, Univ. of Molise, second year)

9. Study Procedure

10. Procedure Overview
1.Participants’ training on the system
2.Presentation of the experiment procedure
3.Manual labeling by participants
4.Automatic labeling
5.Comparison

11. Manual Labeling
• Subjects label each class by selecting 10 words from it
• Time spent on each class annotated
• Offline study, lasted 2 weeks
book
hotel
room
reservation
arrival
departure
smoking
double
card
breakfast
source code file

12. Aggregating manual labeling
Each artifact is labeled using terms selected
by at least 50% of the subjects
book
hotel
room
reservation
arrival
departure
smoking
double
card
breakfast
book
hotel
room
refund
arrival
check
parking
double
suite
group
confirmation
room
reservation
arrival
departure
date
bed
card
payment
spa
room 3
arrival 3
book 2
hotel 2
reservation 2
departure 2
double 2
card 2
book
hotel
room
reservation
arrival
departure
smoking
double
card
breakfast
book
hotel
room
refund
arrival
check
parking
double
suite
group
confirmation
room
reservation
arrival
departure
date
bed
card
payment
spa

13. Automatic Labeling

14. Text Processing
• Extracted words from
• source code + comments
• comments only
• Identifier splitting (camel case)
• Pruned stop words and programming language
keywords
• Stemming (Porter)
• Term indexing using: tf or tf-idf

15. Labeling techniques
• Simple signature: words from class name, method name and
params, attribute names
• VSM: terms ranked according to tf or tf-idf
• Latent Semantic Indexing (LSI)
• Class methods considered as documents
• Words having the highest weight in the LSI space
• Latent Dirichlet Allocation (LDA)
• Different number of topics: 2, #Methods/2, #Methods
• Core words: having highest probability on the overall set
of topics
• Core topics: words from the topic with highest probability

16. Measurements: RQ1
Asymmetric Jaccard to avoid penalizing
automatic approaches
K(Ci) = {t1 . . . tm}
Kmi (Ci) = {t1 . . . th}
overlapmi (Ci) =
|K(Ci) Kmi
(Ci)|
Kmi (Ci)
manual labeling of Ci
automatic labeling of Ci
by technique mi

17. Measurements: RQ2
A) Ability of LDA and LSI to cluster related classes
Open your book, page 0

18. while (windowEnd+1 < sessions.Count)
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bubble.End = sessions[windowEnd].End.Value;
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if (windowStart < sessions.Count)
Proceedings of the
2012 20th IEEE
International Conference on
Program Comprehension
ICPC 2012
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Celebrating 20 Years
Sponsered by
JUNE 11-13

19. Measurements: RQ2
B) Correlation between overlap and time spent by
subjects to label artifacts
H(Ci) =
mX
j=1
tfj
n
· log
✓
n
tfj
◆
n =
Pm
k=1 tfk
A) Ability of LDA and LSI to cluster related classes
measured as Entropy of terms in a class
eH(Ci) = H(Ci)/log(m)normalized as:

20. Results

21. RQ1: eXVantage
Signature (tf)
Signature (tf-idf)
VSM (tf)
VSM (tf-idf)
LSI (tf)
LSI (tf-idf)
LDA (n=M, core_tp)
LDA (n=M, core_ts)
LDA(n=M/2, core_tp)
LDA (n=M/2, core_ts)
LDA (n=2, core_tp)
LDA (n=2, core_ts)
0.00 20.00 40.00 60.00 80.00
59
61
59
57
50
46
52
53
59
61
0
0
59
60
56
56
53
52
63
58
69
70
77
76
Comments+Code Comments only
Overlap

22. RQ1: JHotDraw
Signature (tf)
Signature (tf-idf)
VSM (tf)
VSM (tf-idf)
LSI (tf)
LSI (tf-idf)
LDA (n=M, core_tp)
LDA (n=M, core_ts)
LDA(n=M/2, core_tp)
LDA (n=M/2, core_ts)
LDA (n=2, core_tp)
LDA (n=2, core_ts)
0.00 20.00 40.00 60.00 80.00
52
53
52
53
46
58
44
48
54
53
0
0
62
59
52
60
55
59
55
54
65
60
75
74
Comments+Code Comments only
Overlap

23. Why LDA does not work well
Class distance in eXVantage
topic 1
topic2

24. RQ2: Entropy
Comments do not contain clearly dominant words
!"#$%&"$ !''#&() !''#&()$*&+,
-./--./0-.1--.10
2&(3!4,$!5$(#3')
!"#$%&"$ !''#&() !''#&()$*&+,
-./--./0-.1--.10
2&(3!4,$!5$(#3')
eXVantage JHotDraw
Entropyofterms
Entropyofterms
Code+comments Code+comments Comments onlyComments only

25. RQ2: Effort to label artifacts
System Class size
Comment
verbosity
JHotDraw 0.6 -0.25
eXVantage 0 -0.13
Pearson Correlation
Different comment verbosity in JHotDraw (6) and eXVantage (14)

26. RQ2:VSM vs. LSI
VSM
LSI
0 20 40 60 80
72
59
42
61
Low High
JHotDraw
VSM
LSI
0 20 40 60 80
68
68
52
72
Low High
exVantage
Overlap vs. effort needed to label a class

27. Conclusions