understanding the redundancy! of software systems

Understanding the Redundancy!of Software Systems

Andrea Mattavelli

Research Advisor :!Research Co-Advisor :

Prof. Mauro Pezzè!Prof. Antonio Carzaniga

Redundancy

Informally, a system is redundant when!it is able to perform the same functionality !by executing different code.

“

Software Redundancy

Version 1

Version 2

Version n

Selection!Algorithm

...

Input

Input Checkpoint Execute Version Test

Output

Output

Exception Fail

Restore

Alternatives? FailNo

N-version Recovery Blocks

Yes

Software

Software Redundancy

Version 1

Version 2

Version n

Selection!Algorithm

...

Input

Input Checkpoint Execute Version Test

Output

Output

Exception Fail

Restore

Alternatives? FailNo

N-version Recovery Blocks

Yes

Deliberate

Modern software systems contain a form of redundancy that is indeed intrinsically present.

“Software RedundancyIntrinsic

Intrinsic Redundancy: ExamplesDateTime t = new DateTime(); //... //get the beginning of the day for time tDateTime beginDay = t.millisOfDay().withMinimumValue();

Joda-Time

DateTime t = new DateTime(); //... //get the beginning of the day for time tDateTime beginDay = t.millisOfDay().withMinimumValue(); = t.toDateMidnight().toDateTime(); = t.withTimeAtStartOfDay();

Joda-Time

Intrinsic Redundancy: Examples

Joda-Time

MultiMap m = new MultiMap();//…//check if element is already in mapif (m.contains(x))

Google Guava

Intrinsic Redundancy: ExamplesDateTime t = new DateTime(); //... //get the beginning of the day for time tDateTime beginDay = t.millisOfDay().withMinimumValue(); = t.toDateMidnight().toDateTime(); = t.withTimeAtStartOfDay();

Joda-Time

MultiMap m = new MultiMap();//…//check if element is already in mapif (m.contains(x)) if (m.elementSet().contains(x)) if (m.count(x) > 0)

Google Guava


Joda-Time

MultiMap m = new MultiMap();//…//check if element is already in mapif (m.contains(x)) if (m.elementSet().contains(x)) if (m.count(x) > 0)

Google Guava


0 LOC!(0%)

2 LOC!(~0.1%)

Security

Automatic repair

Test oracles

Self-healing

Studying Intrinsic RedundancyUsing


“Studying Intrinsic RedundancyStudying

What is its essence?Modern software systems contain a form of redundancy that is indeed intrinsically present.


How pervasive is it?

What is its essence?Modern software systems contain a form of redundancy that is indeed intrinsically present.


How pervasive is it?

What is its essence?

How to identify it?



Why is it present?How pervasive is it?

What is its essence?

How to identify it?



What Is Its Essence?

redundancy=

+functional!

equivalenceexecution diversity


redundancy=

+functional!



SA

SB

? ? ?

a1 a2 a3

a1 a2 a3

Observational Equivalence![Hennessy et al.]

redundancy=

+functional!



redundancy=

+functional!



com.google.collect.LinkedlistMap.putAll@216com.google.collect.LinkedlistMap.putAll@226com.google.collect.LinkedlistMap.putAll@227com.google.collect.LinkedlistMap.put@123com.google.collect.LinkedlistMap.put@125com.google.collect.LinkedlistMap.put@126!!!

com.google.collect.LinkedlistMap.put@123com.google.collect.LinkedlistMap.put@125com.google.collect.LinkedlistMap.put@126com.google.collect.LinkedlistMap.put@127com.google.collect.LinkedlistMap.put@132com.google.collect.LinkedlistMap.put@133!!

putAll(K key, Iterable values)put(K key, V value)

How Pervasive Is It?

Joda-Time

GraphStream

SWT


Joda-Time

4700+!equivalent method sequences

GraphStream

SWT


Intrinsic redundancy

redundancy=

+functional!



SA

SB

? ? ?

a1 a2 a3

a1 a2 a3





How Pervasive Is It?redundancy

=

+functional!



SA

SB

? ? ?

a1 a2 a3

a1 a2 a3






How to Identify It?

pop()

Object o = s.peek();int index = s.size();index = index - 1;s.remove(index);return o;

Stack s = new Stack();s.push(0);s.push(1);!Stack s = new Stack();s.push(-174);

Execution Scenarios

redundancy=

+functional!



SA

SB

? ? ?

a1 a2 a3

a1 a2 a3






How to Identify It?

pop()

Object o = s.peek();int index = s.size();index = index - 1;s.remove(index);return o;

Stack s = new Stack();s.push(0);s.push(1);!Stack s = new Stack();s.push(-174);

Execution Scenarios

Design for reusability

Non-functional requirements

Replicated Functionalities

Backward compatibility

Why?

redundancy=

+functional!



SA

SB

? ? ?

a1 a2 a3

a1 a2 a3





understanding the redundancy! of software systems

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