Empirical software engineering is five years old

March 31, 2011
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(This article was first published on The Shape of Code » R, and kindly contributed to R-bloggers)

Science and engineering are built on theoretical models that are tested against measurements of ‘reality’. Until around 10 years ago there was very little software engineering ‘reality’ publicly available; companies rarely made source available and were generally unforthcoming about any bugs that had been discovered. What happened around 10 years ago was the creation of public software repositories such as SourceForge and public fault databases such as Bugzilla. At last researchers had access to what could be claimed to be real world data.

Over the last five years there has been an explosion of papers using SourceForge/Bugzilla kinds of data looking for a connection between everything+kitchen sink and faults. The traditional measures such as Halstead and McCabe have not stood up well against this onslaught of data, hardly surprising given they were more or less conjured out of thin air. Some researchers are trying to extract information about developer characteristics from mailing lists; given that software is written by developers there is obviously a real need for the characteristics of major project contributors to play a significant role in any theory of software faults.

Software engineering data includes a lot more than what can be extracted from source code, bug lists and email lists. A growing number of repositories have been set up to hold measurement and experimental data, e.g., hardware failures, effort prediction (while some of this data is pre-2000 it tends to be low volume or poor quality), and file system related.

At the individual level a small number of researchers have made data available on their own web site, a few more will send a copy if asked and sadly there are many cases where the raw data has been lost. In two recent cases researchers have responded to my request for raw data by telling me they are working on additional papers and don’t want to make the data public yet. I can understand that obtaining interesting data requires a lot of work and researchers want to extract maximum benefit; I look forward to see the new papers and the eventual availability of the data.

My interest in all this data is that I have started work on a book covering empirical software engineering using R. Five years ago such book would have contained lots of equations, plenty of hand waving and if data sets were available they would probably have been small enough to print on one page. Today there are still plenty of equations (mostly relating to statistical this that and the other), no hand waving (well, none planned), data sets for everything covered (some in the gigabytes and a few that can still fit on a page) and pretty pictures (color graphs, as least for the pdf version).

When historians trace back the history of empirical software engineering I think they will that it started for real sometime around 2005. Before then any theories that were based on observation tended to have small, single study, data sets with little statistical significance or power.

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