Presentation at 10th International Conference on Generative Programming and Component Engineering (GPCE 2011)

1. On the Impact of Feature
Dependencies when Maintaining
Preprocessor‐based
So<ware Product Lines
Márcio Ribeiro Felipe Queiroz Paulo Borba
Társis Tolêdo Claus Brabrand Sérgio Soares
{mmr3, Cq, phmb, twt, scbs}@cin.ufpe.br
brabrand@itu.dk

2. Virtual SeparaKon of Concerns (VSoC)
2

3. But not enough for Feature Modularity…
3

4. Problem
 Developers can introduce compila?on and behavioral
errors to features due to feature dependencies…
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5. … leading to lower producKvity
 Late error detecKon
 Developers discover the problem only when compiling and
execu?ng the problema?c product
 Difficult navigaKon
 Developers not aware of feature dependencies
 Even worse when using VSoC: features are hidden!
5

6. To minimize these
problems:
Emergent Interfaces
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7. Emergent Interfaces in a nutshell
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8. Dependencies captured! Developers can
focus on the impacted features…
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9. Feature dependencies
can cause problems
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10. Emergent Interfaces
complement VSoC
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11. Agenda
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12. Study secngs
 43 Preprocessor‐based SoMware Product lines
 Java and C
 Different sizes and domains
 Script tool for compu?ng two metrics:
 MDi: number of methods with preprocessor direc?ves
 MDe: number of methods with feature dependencies
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13. Feature dependencies our tool considers
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14. Effort esKmaKon:
VSoC vs. Emergent Interfaces
Number of Fragments
Number of Features
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15. Methods selecKon
 Randomly methods selec?on
 Only methods that contain the feature dependencies
we focus on this work
 Which methods should we select?
 Many fragments: favoring emergent interfaces
 Few fragments: no differences
15

16. Groups
 Two groups:
 Why 2 as a threshold?
 Differences between both approaches appear from 2
 1: both approaches have always the same effort es?ma?on
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17. Methods selecKon to fit the groups
 Propor?onal selec?on according to each SPL
 Example: libxml2
 Group 1: 953 methods (8 methods selected)
 Group 2: 125 methods (1 method selected)
 Majority (23 product lines)
 1:1
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18. General algorithm for effort esKmaKon
 While we do not reach 3 replica?ons
 For each product line
 Randomly select methods propor?onally according to the
groups
 For each method
 Randomly select a variable
 From this variable, compute NoFa, NoFe, and LOC for both
approaches
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19. Results
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20. QuesKon 1: how oMen
methods with preprocessor
direc?ves contain feature
dependencies?
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21. Frequency of feature dependencies
Methods with Dependencies
Methods with DirecKves
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22. Our data reveal that…
 Methods with direc?ves that also contain the
feature dependencies we studied:
 Max: 88% (mobile‐rss)
 Min: 12% (lampiro)
 So, the feature dependencies we considered may
be common in the 43 SPLs we analyzed
 Only 6 SPLs have MDe/MDi < 50%
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23. QuesKon 2: how feature
dependencies impact
maintenance effort when
using VSoC and emergent
interfaces?
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24. SelecKon: methods, groups, SPLs
 For each replica?on: 115 methods
 Methods selec?on according to each product line
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25. Emergent Interfaces effort esKmaKon
 Effort es?ma?on in all SPLs
 Methods distribu?on by groups:
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26. When increasing the number of
fragments…
 … the percentage of methods where Emergent
Interfaces achieve effort reduc?on also increases…
100%
EsKmaKon of Effort reducKon
95%
90%
85%
Replica?on 1
80% Replica?on 2
Replica?on 3
75%
70%
65%
> 2 > 3 > 4 > 5 > 6
Number of Fragments 26

27. Threats to validity
 Metrics and effort es?ma?on
 Time beher measures effort…
 … but the metrics are s?ll useful
 Overhead to compute emergent interfaces
 Dependencies
 Interprocedural, chain of assignments… (not computed)
 So, the numbers we presented might be even higher…
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28. Concluding remarks
 How
oMen the feature dependencies we analyzed
occur in prac?ce?
 Max: 88%; Min: 12%; Majority > 50%
 Emergent interfaces can achieve effort reduc?on
 For the majority of the studied methods (65%): same
effort of VSoC
 Nega?ve impact of VSoC is not so common
 More
significant effort reduc?ons: methods with
many fragments (Group 1)
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