History analysis
Tudor Gîrba
www.tudorgirba.com

Herodotus … displays his enquiry, so that human
achievements may not become forgotten … and great and
marvelous deeds … may not be without their glory …
especially to show why the two peoples fought with each
other.
He rodotus

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History holds useful information

History holds useful information
When did it change?

1
hman etal, 200
Le

Spectographs show change activity
commit
time
4
Wu etal, 200

History holds useful information
When did it change?
How did it change?

Evolution Matrix shows changes in classes
Idle class
Pulsar class
Supernova class
White dwarf class
as se, 2002
Lan za, Duc

History holds useful information
When did it change?
How did it change?
What changed?

2 4 3 5 7
2 2 3 4 9
2 2 1 2 3
2 2 2 2 2
1 5 3 4 4

Evolution of
Number of Methods LENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 2i-n
LENOM(C) = 4 + 2 + 1 + 0 = 7
1 5 3 4 4

Latest Evolution of
Number of Methods LENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 2i-n
Earliest Evolution of
Number of Methods EENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 22-i
-3 -2 -1 0
LENOM(C) = 42 + 22 + 12 + 02 = 1.5
1 5 3 4 4
EENOM(C) = 4 20 + 2 2-1 + 1 2-2 + 0 2-3 = 5.25

ENOM LENOM EENOM
2 4 3 5 7 7 3.5 3.25
2 2 3 4 9 7 5.75 1.37
2 2 1 2 3 3 1 2
2 2 2 2 2 0 0 0
1 5 3 4 4 7 1.25 5.25

ENOM LENOM EENOM
balanced changer 7 3.5 3.25
late changer 7 5.75 1.37
3 1 2
dead stable 0 0 0
early changer 7 1.25 5.25

History can be measured in many ways
Evolution Number of Methods
Stability Number of Lines of Code
Historical Max of Cyclomatic Complexity
Growth Trend Number of Modules
... ...

History holds useful information
When did it change?
How did it change?
What changed?
What will change?

The recently changed parts are likely to change in the
near future
n wisdom
Commo

The recently changed parts are likely to change in the
near future
e they really?
Ar
n wisdom
Commo

30% 90%

present

past
present

past future
present

past future
present

past future
present

past future
prediction hit present

Yesterday’s Weather shows the locality of changes
hit hit hit
YW = 3 / 8 = 37%
hit hit hit hit hit hit hit
YW = 7 / 8 = 87%
tal, 2004
Girba e

Co-change analysis recovers hidden dependencies
8
Gall etal 199

eRose suggests files to co-change
5
rmann etal 200
Zimme

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?

2
Eick etal 200

CVSscan shows fine grained changes
e tal 2005
Voinea

Kumpel offers a different view on how files change
8
Jun ker 200

CVS shows activity

Who is responsible for this?

Who is responsible for this?

Alphabetical order is no order

Ownership Map reveals development patterns
tal, 2006
Girba e

JEdit

Ant

Who copied from whom?
(john 23.06.03) public boolean stillValid (ToDoItem I, Designer dsgr) {
(bill 09.01.05) if (!isActive()) {
(bill 09.01.05) return false
(bill 09.01.05) }
(steve 16.02.05) List offs = i.getOffenders();
(john 23.06.03) Object dm = offs.firstElement();
(steve 16.02.05) ListSet newOffs = computeOffenders(dm);
(john 23.06.03) boolean res = offs.equals(newOffs);
(john 23.06.03) return res;
(george 13.02.05) public boolean stillValid (ToDoItem I, Designer dsgr) {
(bill 11.13.05) if (!isActive()) {
(bill 11.13.05) return false
(bill 11.13.05) }
(steve 16.02.05) List offs = i.getOffenders();
(george 13.02.05) Object dm = offs.firstElement();
(steve 16.02.05) ListSet newOffs = computeOffenders(dm);
(george 13.02.05) boolean res = offs.equals(newOffs);
(george 13.02.05) return res;

Who copied from whom?
(john 23.06.03) public boolean stillValid (ToDoItem I, Designer dsgr) {
(bill 09.01.05) if (!isActive()) {
(bill 09.01.05) return false
(bill 09.01.05) }
(steve 16.02.05) List offs = i.getOffenders();
(john 23.06.03) Object dm = offs.firstElement();
(steve 16.02.05) ListSet newOffs = computeOffenders(dm);
(john 23.06.03) boolean res = offs.equals(newOffs);
(john 23.06.03) return res;
(george 13.02.05) public boolean stillValid (ToDoItem I, Designer dsgr) {
(bill 11.13.05) if (!isActive()) {
(bill 11.13.05) return false
(bill 11.13.05) }
(steve 16.02.05) List offs = i.getOffenders();
(george 13.02.05) Object dm = offs.firstElement();
(steve 16.02.05) ListSet newOffs = computeOffenders(dm);
(george 13.02.05) boolean res = offs.equals(newOffs);
(george 13.02.05) return res;

When did changes happen?
23.06.03 public boolean stillValid (ToDoItem I, Designer dsgr) {
09.01.05 if (!isActive()) {
09.01.05 return false
09.01.05 }
16.02.05 List offs = i.getOffenders();
23.06.03 Object dm = offs.firstElement();
16.02.05 ListSet newOffs = computeOffenders(dm);
23.06.03 boolean res = offs.equals(newOffs);
23.06.03 return res;
13.02.05 public boolean stillValid (ToDoItem I, Designer dsgr) {
11.13.05 if (!isActive()) {
11.13.05 return false
11.13.05 }
16.02.05 List offs = i.getOffenders();
13.02.05 Object dm = offs.firstElement();
16.02.05 ListSet newOffs = computeOffenders(dm);
13.02.05 boolean res = offs.equals(newOffs);
13.02.05 return res;

Clone Evolution shows how developers copy
tal, 2006
Balint e

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?
How to model structure changes?

{ {
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A large system contains lots of details

{ { { { { { { { { {
{ { { { { { { { { {
} } } } }
}
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} }
} }
} }
}
} { } } { } } { } } { } } { }
Its history contains even more details

{ { { { { { { { { {
{ { { { { { { { { {
} } } } }
}
} }
} }
} }
} }
}
} { } } { } } { } } { } } { }
And lots of details are difficult to analyze

e.g., Evolution Matrix
Idle
class
Pulsar
class
Supernova
class
attributes
White dwarf
class methods Class

e.g., Evolution Matrix
Idle
class
Pulsar
class
Supernova
class
NOA
White dwarf
class NOM Class

e.g., Evolution Matrix
Idle
class
Pulsar
class
Supernova
class
NOA
White dwarf
class NOM Class

e.g., Evolution Matrix
Idle
class history
Pulsar
class history
Supernova
class history
ClassHistory
White dwarf isPulsar
class history isIdle
...

System
Version
Class
Version

System
Version
Class Class
History Version

System System
History Version
Class Class
History Version

System System
History Version
Class Class
History Version

System System
History Version
en tity
st c lass 200
5
as fir Gir ba,
his tory
mo dels
His mo
Class Class
History Version

2 4 3 5 7
2 2 3 4 9
2 2 1 2 3
2 2 2 2 2
1 5 3 4 4

Evolution of
Number of Methods LENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 2i-n
LENOM(C) = 4 + 2 + 1 + 0 = 7
1 5 3 4 4

Latest Evolution of
Number of Methods LENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 2i-n
Earliest Evolution of
Number of Methods EENOM(C) = ∑ |NOMi(C)-NOMi-1(C)| 22-i
-3 -2 -1 0
LENOM(C) = 42 + 22 + 12 + 02 = 1.5
1 5 3 4 4
EENOM(C) = 4 20 + 2 2-1 + 1 2-2 + 0 2-3 = 5.25

past future
present

past future
YesterdayWeatherHit(present):
present

past future
YesterdayWeatherHit(present):
past:=histories.topLENOM(start, present)
present

past future
YesterdayWeatherHit(present):
past:=histories.topLENOM(start, present)
future:=histories.topEENOM(present, end)
present

past future
YesterdayWeatherHit(present):
past:=histories.topLENOM(start, present)
future:=histories.topEENOM(present, end)
past.intersectWith(future)
present

past future
YesterdayWeatherHit(present):
past:=histories.topLENOM(start, present)
future:=histories.topEENOM(present, end)
past.intersectWith(future).notEmpty()
prediction hit present

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?
How to model structure changes?
How to combine time with structure?

Detection Strategies are metric-based queries to
detect design flaws
Rule 1
METRIC 1 > Threshold 1
AND Quality problem
Rule 2
METRIC 2 < Threshold 2

e.g., a God Class centralizes too much intelligence
Class uses directly more than a
few attributes of other classes
ATFD > FEW
Functional complexity of the
class is very high
AND GodClass
WMC ! VERY HIGH
Class cohesion is low
TCC < ONE THIRD

e.g., a God Class centralizes too much intelligence
Class uses directly more than a
few attributes of other classes
ATFD > FEW
Functional complexity of the
class is very high
AND GodClass
WMC ! VERY HIGH
sta ble?
it is
Class cohesion is low
t if
TCC < ONE THIRD
ut, wha
B

God Class
in the last version
isGodClass(last)
AND Harmless God Class
Stable throughout
the history
Stability > 90%
4
Ratiu etal, 200

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?
How to model structure changes?
How to combine time with structure?
How to model changes in relationships?

What happens with inheritance?
A A A A A
B C B C B C B B
D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5
A is persistent, B is stable, C was removed, E is newborn ...

History contains too much data
A A A A A A A A A A A A A A A A A A A A
B C B C B C B B B C B C B C B B B C B C B C B B B C B C B C B B
D D D E D D D E D D D E D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5
A A A A A A A A A A A A A A A A A A A A
B C B C B C B B B C B C B C B B B C B C B C B B B C B C B C B B
D D D E D D D E D D D E D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5
A A A A A A A A A A A A A A A A A A A A
B C B C B C B B B C B C B C B B B C B C B C B B B C B C B C B B
D D D E D D D E D D D E D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5
A A A A A A A A A A A A A A A A A A A A
B C B C B C B B B C B C B C B B B C B C B C B B B C B C B C B B
D D D E D D D E D D D E D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5 ver .1 ver. 2 ver. 3 ver. 4 ver. 5

System System
History Version
Class Class
History Version

System System
History Version
Inheritance
Version
Class Class
History Version

System System
History Version
Inheritance Inheritance
History Version
Class Class
History Version

What happens with inheritance?
A A A A A
B C B C B C B B
D D D E
ver .1 ver. 2 ver. 3 ver. 4 ver. 5
A is persistent, B is stable, C was removed, E is newborn ...

A
changed
methods
changed
age
lines
C B
Removed
Removed
D E
A is persistent, B is stable, C was removed, E is newborn ...

Hierarchy Evolution reveals patterns
tal, 2005
Girba e

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?
How to model structure changes?
How to combine time with structure?
How to model changes in relationships?
How to model co-changes?

y relat ionships
re n-ar
Co-ch anges a
1 2 3 4 5 6
A
A
B
B E
C
D
E C D

1 2 3 4 5 6
A
B
C
D
Version
E

1 2 3 4 5 6
A
B
C
D
Version
E changed

1 2 3 4 5 6
A History
changed(i)
B
C
D
Version
E changed

What is Formal Concept Analysis?

1 2 3 4 5 6
A
B
C
D
E

{A, B, C, D, E}
1 2 3 4 5 6 Ø
A {A, D, E} {A, B, C, D}
{2} {6}
B
{D, E} {A, D} {A, B, C}
C FCA
{2, 4} {2, 6} {5, 6}
D
{D} {A} {C}
E {2, 4, 6} {2, 5, 6} {3, 5, 6}
Ø
{1, 2, 3, 4, 5, 6}

{A, B, C, D, E}
1 2 3 4 5 6 Ø
A {A, D, E} {A, B, C, D}
{2} {6}
B
{D, E} {A, D} {A, B, C}
C FCA
{2, 4} {2, 6} {5, 6}
D
{D} {A} {C}
E {2, 4, 6} {2, 5, 6} {3, 5, 6}
Ø
{1, 2, 3, 4, 5, 6}
irba e tal 2007
G

Parallel Inheritance
add simultaneously children to several classes
Shotgun Surgery
change several classes simultaneously, but do not add methods

System System
History Version
Inheritance Inheritance
History Version
Class Class
History Version

System System
History Version
Inheritance Inheritance
History Version
Class Class
History Version

History Version
History Version
History Version

History holds useful information
When did it change?
How did it change?
What changed?
What will change?
Who did what?
How to model history?
How to model structure changes?
How to combine time with structure?
How to model changes in relationships?
How to model co-changes?
Issues
How to sample history?
What to capture?
How to represent it?

{
{
} }
}
{
{
{
}
}
re
v er
se
en
gin
ee
rin
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reverse engineering
fo
actual development rw
ar
d
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gin
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rin
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{
{
}
}
{
{
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}

Tudor Gîrba
www.tudorgirba.com
creativecommons.org/licenses/by/3.0/