IWSM Presentation

1. On Automatically Collectable Metrics
for Software
Maintainability Evaluation
Jan-Peter Ostberg
&
Stefan Wagner

2. Maintenance Worker
Assessment of
Maintenance Work

3. (metrics maintenance) OR
(maintenance measure) AND
Software OR
maintainability

4. 12
11
10
9
8
7
6
5
4
3
2
1
0

5. What defines a good measure?

6. Easy to understand…
…, but also accurate.

7. Easy to Use

8. Often mentioned metrics…
… but not practical ones.

9. McCabe
if( P1 ){
if( P2 ){
expression2;
}else{
expression3;
}else{
expression1;}
if((P1 && P2 && !P3)||(P1 && P3 && P4)){
if((P5 && P6 && P7)||(!P5 && !P7)){
expression2;
}else{
expression3;
}else{
expression1;}
Code on bottom is
clearly more complex.
McCabe for both = 3

10. Halstead Software Science
Program Volume: V = N x log2 h
h N
1 2
2 h
2
D  
Implementation time:
D V
18
T


18
elementary
decisions per
second
Difficulty of a Program:

11. Lines of Code
What is the LoC value here?
public String tellMeEqual (int a, int b){
String result = „undefined“;
if (a > b){
result = „a is larger“;
} else {
if(a == b) {
result = „a is equal“;
} else {
result = „b is larger“;
}
}
return result;
}
13?
5?

12. Lines of Code

13. Maintainability Index
HalsteadVolume McCabe
 171  5.2  ln( )  0.23

LoC CommentPercentage
    
16.2 ln( ) (50 sin( 2.46 )
))
100
171
Simplified Version:
 MAX(0, (1715.2log(HalsteadVolume) 0.23McCabe16.2log(LoC)

14. We need
better
ways to
measure
our
software!

15. Suggestion: Nesting Depth
if(P==1){
expression1;
}else{
if(P==2){
expression2;
}else{
if(P==3){
expression3;}
}
}
Nesting depth = 3
Switch(P){
case 1:
expression1;
break;
case 2:
expression2;
break;
case 3:
expression3;
break;}
Nesting depth = 1

16. giphy.com
Suggestion: Clone-Ration
„…every second
unintentional
inconsistency between
clones constitutes to a
fault…”
Juergens et al. „Do code clones matter?“

17. Suggestion: Bug-Patterns
• Bug-Detection-Tools
are getting really
good.
• Low amount of
findings implies
better
maintainability

18. Suggestion: Test Results and Coverage
http://testing.gobanana.co.uk
• More tests + high
coverage implies code is
test-friendly
• Ignored test results are
a hint for not
understood code parts
• Tests encourage the
maintenance of code

19. Conclusion
• The blindfolded usage of maintenance metrics is problematic.
• There are useful and accurate maintenance metrics.
• The metrics should be collected automatically.

20. For more, please read our paper!

21. Thank you for your attention!