Biological modeling of software development dynamics

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Biological modeling of software development dynamics

  1. 1.  Software development can be treated as an optimization problem: maximise software quality subject to the constraints limited resources Software quality: number of features, performance, reliability, etc.  Resources: time, money, etc. 
  2. 2.  Questions to answer: › How long it will take to complete a particular task? › How long it will take to test a particular module? › How many defects remain in a particular module after a release? › At a particular time, what portion of resources should be devoted to testing as opposed to developing new features?
  3. 3.  How to answer the previous questions: › By building a model  Purpose of modelling › Predict, explain, discover, guide  Modelling is a two-steps process: › Determine set of variables of interests › Determine set of equations to describe how these variables change and which kinds of relations exist among them
  4. 4. Software development is an iterative process  The process of software developement can be described by the phrase evolution of software  The phrase implies similarities with evolution of biological systems  How can we use this fact? – central idea of this presentation 
  5. 5.  Bio-inspired optimization algorithms: › Genetic algorithm – motivated by Darwin’s › › › › principal of natural selection Memetic algorithm – motivated by genetic + experience Particle swarm optimization – motivated by behavior of a flock of birds Ant colony optimization – motivated by behavior of an ant-colony Bee-inspired optimization, shuffled frog leaping algorithm, etc.
  6. 6.  Artificial neural networks › It is computational structure inspired by central nervous system  Artificial immune system › It is computationally intelligent systems inspired by the principles of the immune system  Capture-recapture bug-estimation method › Statistical method developed for population estimation in bio-ecosystems
  7. 7.    Accepted among most major software companies (Google, Facebook, Mozilla and Microsoft) Main principle - abandon long development cycles in favor of faster releases in order to bring the latest features and fixes to end-users Information for making decision if software is ready for a new release: › Relationship between number of bugs in the system (b(t)) and effort necessary to resolve them (e(t)). › The more effort is spent on defect resolving, the less time is left for developing new features.
  8. 8.  O1 – Increasing (or decreasing) of e(t) leads to decreasing (or increasing) of b(t): e(t )  e(t ) b(t ) O2 – Increasing (or decreasing) of b(t) requires increasing (or decreasing) of e(t): b(t )  b(t ) e(t ) b(t ) e(t ) O3 – As a result from the previous two observation, both b(t) and e(t) exhibit periodic oscillations.
  9. 9. O4 – The relationship from O1and O2 is not linear.  O5 – Small increase of effort can lead to significant reduction of defects number.  O6 –Pareto principle – majority of time is spent on small number of difficult bugs (approximately, removal of 30% of bugs requires 70% of time). 
  10. 10. O7 – Changes in code churn exhibits growth rate which can be modeled by sigmoid function.  O8 – b(t) increasing is steeper than decreasing.  O9 – e(t) decreasing is steeper than increasing.  Observations O1-O9 imply similarity with predator-prey ecosystem  › Predator – tester, programmer › Prey - bugs
  11. 11.  Most famous predator prey model expressed by: db(t ) dt  b( e) de(t ) dt e( b) Main characteristics: › In the case e(t)=0 (no hunt for bugs), b(t) has exponential growth. › The rate of detecting and reducing number of bugs by developers/testers is proportional to the number of bugs and effort invested in bug reduction (βeb). Intuitively, if there are more bugs in the system, it will be easier to detect and eliminate some of them. In addition, if more effort is invested in bugs reduction, the more bugs will be reduced.
  12. 12. › In the absence of bugs (b(t)=0), effort exponentially reduces to zero. › The rate at which the effort grows is proportional to the rate at which the developers/testers encounter bugs.  Issues with the presented model: › Extremely sensitive to small perturbations › Allows unlimited exponential growth of number of bugs › Unlimited ability of a single developer/tester to detect and eliminate bugs
  13. 13.  Improvement of LV model which resolves previous issues: db(t ) dt b b(1 ) K b b k e de(t ) dt e b b k e Number of bugs is limited by the size and complexity of a project which is specified by the parameter K.  Rate at which a single developer/tester detects and removes bugs is limited. 
  14. 14.   Relationship among parameters defines two main regions. Model allows regular oscillations (suitable for the beginning and the middle of project) as well as dumped oscillations (suitable for project near completion)
  15. 15.  Normalized values of e(t) and b(t) Conclusions: › The model was evaluated on real-life small size project developed under RR methodology › The model fairly accurately captures observations O1-O9 › Future work: investigate if the results can be generalized for description of projects with different characteristics.

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