Time+Place: | Tuesday 01/05/2012 14:30 Room 337-8 Taub Bld. |

Title: | How Do Classes Choose Their Parents? (Preferential Attachment to the Trial) |

Speaker: | Yossi Gil http://www.cs.technion.ac.il/people/yogi/ |

Affiliation: | Computer Science, Technion |

Previous research repeatedly discovered a power-law distribution of object-oriented software metrics. The classical process of preferential attachment was proposed as a possible explanation. In this presentation, I will describe research in progress which tries to evaluate this conjecture: we focus on the famous Number of Children (NOC) object-oriented software metric, that is, the number of immediate sub-classes a given class has. We examine the history of development of several software artifacts in attempt to asses hypothesis underlying preferential attachment, namely that the number of existing children a class already has, determines the probability it is selected as a parent again. Each history is converted to a large system of high-degree polynomial equations whose solution provides the desired probabilities. We describe a numerical method for solving this system, and employing it, we are able to reason about dependencies. Our finding give empirical support for the preferential attachment hypothesis. However we identify a number of equal or better predictors of this probability, including the class's age, i.e., how recently it was changed. The strongest and unequivocal predictor turns out to be the total number of changes the class went through. Work carried out in cooperation with Sabih Agbaria, Irad Yavneh and Amnon J. Meir Short Bio: Yossi Gil is is on the faculty of the department of computer science at the Technion. Refreshments served from 14:15 on, Lecture starts at 14:30