Network analysis of dependency graphs between code components can help predict defects and prioritize testing. Analyzing dependencies captured metrics like centrality and ego networks that strongly correlated with past defects. These network measures improved prediction of defects, ranking highest risk binaries, and identification of critical "escrow" binaries requiring extra testing over complexity metrics alone, doubling recall of escrow binaries. Combining network and complexity analyses provides more effective defect prediction and testing prioritization to aid new QA managers.

1. Predicting Defects
using Network Analysis
on Dependency Graphs
Thomas Zimmermann, University of Calgary, Canada
Nachiappan Nagappan, Microsoft Research, USA

2. Bugs are everywhere

3. Bugs are everywhere

4. Bugs are everywhere

5. Quality assurance is limited...
...by time...

6. Quality assurance is limited...
...by time... ...and by money.

7. Spent resources on the
components that need it most,
i.e., are most likely to fail.

8. Meet Jacob

9. Meet Jacob
• Your QA manager

10. Meet Jacob
• Your QA manager
• Ten years knowledge
of your project

11. Meet Jacob
• Your QA manager
• Ten years knowledge
of your project
• Aware of its history
and the hot spots

12. But then Jacob left...

13. Meet Emily
• Your new QA manager
(replaces Jacob)
• Not much experience
with your project yet
• How can she allocate
resources effectively?

14. Meet Emily
• Your new QA manager
(replaces Jacob)
• Not much experience
with your project yet
• How can she allocate
resources effectively?

15. Indicators of defects
• Code complexity
- Basili et al. 1996, Subramanyam and Krishnan 2003,
- Binkley and Schach 1998, Ohlsson and Alberg 1996, Nagappan et al. 2006

16. Indicators of defects
• Code complexity
- Basili et al. 1996, Subramanyam and Krishnan 2003,
- Binkley and Schach 1998, Ohlsson and Alberg 1996, Nagappan et al. 2006
• Code churn
- Nagappan and Ball 2005

17. Indicators of defects
• Code complexity
- Basili et al. 1996, Subramanyam and Krishnan 2003,
- Binkley and Schach 1998, Ohlsson and Alberg 1996, Nagappan et al. 2006
• Code churn
- Nagappan and Ball 2005
• Historical data
- Khoshgoftaar et al. 1996, Graves et al. 2000, Kim et al. 2007,
- Ostrand et al. 2005, Mockus et al. 2005

18. Indicators of defects
• Code complexity
- Basili et al. 1996, Subramanyam and Krishnan 2003,
- Binkley and Schach 1998, Ohlsson and Alberg 1996, Nagappan et al. 2006
• Code churn
- Nagappan and Ball 2005
• Historical data
- Khoshgoftaar et al. 1996, Graves et al. 2000, Kim et al. 2007,
- Ostrand et al. 2005, Mockus et al. 2005
• Code dependencies
- Nagappan and Ball 2007, Schröter et al. 2006
- Zimmermann and Nagappan 2007

19. Centrality

20. Hypothesis
Network measures on dependency graphs
- correlate with the number of post-release defects (H1)
- can predict the number of post-release defects (H2)
- can indicate critical “escrow” binaries (H3)

21. DATA. .

22. 2252 Binaries
28.3 MLOC

23. Windows Server layout

24. Windows Server layout

25. Windows Server layout

26. Windows Server layout

27. Data collection
Release point for
Windows Server 2003

28. Data collection
Release point for
Windows Server 2003
Complexity Metrics
Dependencies
Network Measures

29. Data collection
six months
Release point for
to collect
Windows Server 2003
defects
Complexity Metrics
Dependencies
Network Measures Defects

30. Dependencies
• Directed relationship between two pieces
of code (here: binaries)
• MaX dependency analysis framework
-Caller-callee dependencies
- Imports and exports
- RPC, COM
- Runtime dependencies (such as LoadLibrary)
- Registry access
- etc.

31. Centrality
• Degreethe number dependencies
centrality
-
counts
• Closeness centrality binaries into account
-
takes distance to all other
- Closeness: How close are the other binaries?
- Reach: How many binaries can be reached (weighted)?
- Eigenvector: similar to Pagerank
• Betweenness centrality paths through a binary
-
counts the number of shortest

32. Structural holes
A
B
C
No structural hole

33. Structural holes
A A
B B
C C
No structural hole No structural hole
between B and C

34. Ego networks
EGO

35. Ego networks
EGO
INOUT

36. Ego networks
EGO
IN
INOUT

37. Ego networks
EGO
IN OUT
INOUT

38. Complexity metrics
Group Metrics Aggregation
Module metrics # functions in B
for a binary B # global variables in B
# executable lines in f()
# parameters in f()
Per-function metrics Total
# functions calling f()
for a function f() Max
# functions called by f()
McCabe’s cyclomatic complexity of f()
# methods in C
# subclasses of C
OO metrics Total
Depth of C in the inheritance tree
for a class C Max
Coupling between classes
Cyclic coupling between classes

39. RESULTS. .

40. 1 PATTERNS

41. Star pattern
With defects
No defects

42. Undirected cliques
... ...

43. Undirected cliques

44. Undirected cliques
Average number of defects is
higher for binaries in large cliques.

45. 2 PREDICTION

46. Prediction
Model
Input metrics and measures Prediction
PCA
Regression

47. Prediction
Model
Input metrics and measures Prediction
PCA
Regression
Metrics
SNA
Metrics+SNA

48. Prediction
Model
Input metrics and measures Prediction
PCA
Regression
Metrics Classification
SNA
Metrics+SNA Ranking

49. Classification
Has a binary a defect or not?
or

50. Ranking
Which binaries have the most defects?
or or ... or

51. Random splits

52. Random splits
4×50×

53. Classification
(logistic regression)

54. Classification
(logistic regression)
SNA increases the recall by 0.10 (at p=0.01)
while precision remains comparable.

55. Ranking
(linear regression)

56. Ranking
(linear regression)
SNA+METRICS increases the correlation
by 0.10 (significant at p=0.01)

57. 3 ESCROW

58. Escrow binaries
• Escrowcritical binaries for Windows Server 2003
binaries
-list of
- development teams select binaries for escrow based
on (past) experience
• Special protocol for escrow binaries
-involves more testing, code reviews

59. Predicting escrow binaries
Network measures Recall
GlobalInClosenessFreeman 0.60
GlobalIndwReach 0.60
EgoInSize 0.55
EgoInPairs 0.55
EgoInBroker 0.55
EgoInTies 0.50
GlobalInDegree 0.50
GlobalBetweenness 0.50
... ...
Complexity metrics Recall
TotalParameters 0.30
TotalComplexity 0.30
TotalLines 0.30
TotalFanIn 0.30
TotalFanOut 0.30
... ...

60. Predicting escrow binaries
Network measures Recall
GlobalInClosenessFreeman 0.60
GlobalIndwReach 0.60
EgoInSize 0.55
EgoInPairs 0.55
EgoInBroker 0.55
EgoInTies 0.50
GlobalInDegree 0.50
GlobalBetweenness 0.50
... ...
Complexity metrics Recall
TotalParameters 0.30
TotalComplexity 0.30
TotalLines 0.30
TotalFanIn 0.30
Network measures predict twice as 0.30
many
TotalFanOut
... escrow binaries as complexity metrics do.
...

61. CONCLUSION. .
• Classification measures is 0.10 higher than for
-Recall for network
complexity metrics.
- The precision remains comparable.
• Ranking network mesures with complexity metrics
-Combining
increases the correlation by 0.10.
• Escrow metrics fail to predict escrow binaries.
- Complexity
- Network measures predict 60% of escrow binaries.