Archive for March, 2011

Empirical software engineering is five years old

March 31st, 2011 2 comments

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 say 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.

A change of guard in the C standard’s world?

March 17th, 2011 2 comments

I have just gotten back from the latest ISO C meeting (known as WG14 in the language standard’s world) which finished a whole day ahead of schedule; always a good sign that things are under control. Many of the 18 people present in London were also present when the group last met in London four years ago and if memory serves this same subset of people were also attending meetings 20 years ago when I traveled around the world as UK head of delegation (these days my enthusiasm to attend does not extend to leaving the country).

The current convenor, John Benito, is stepping down after 15 years and I suspect that many other active members will be stepping back from involvement once the current work on revising C99 is published as the new C Standard (hopefully early next year meaning it will probably be known as C12).

From the very beginning the active UK participants in WG14 have held one important point of view that has consistently been at odds with a view held by the majority of US participants; we in the UK have believed that it should be possible to deduce the requirements contained in the C Standard without reference to any deliberations of WG14, while many US participants have actively argued against what they see as over specification. I think one of the problems with trying to change US minds has been that the opinion leaders have been involved for so long and know the issues so well they cannot see how anybody could possible interpret wording in the standard in anything other than the ‘obvious’ way.

An example of the desire to not over specify is provided by a defect report I submitted 18 years ago, in particular question 19; what does:

#define f(a) a*g
#define g(a) f(a)

expand to? There are two possibilities and WG14 came to the conclusion that both were valid macro expansions, making the behavior unspecified. However, when it came to a vote the consensus came down on the side of saying nothing about this case in the normative body of the standard, the only visible evidence for this behavior being a bulleted item added to the annex containing the list of unspecified behaviors.

A new member of WG14 (he has only been involved for a few years) spotted this bulleted item that had no corresponding text in the main body of the standard, tracked down the defect report that generated it and submitted a new defect report asking for wording to be added. At the meeting today the straw poll of those present was in favor of adding an appropriate example to C12 {I will link to the appropriate paper once it appears on the public WG14 site}. A minor victory on the road to a full and complete specification.

It will be interesting to see what impact a standing down of the old guard, after the publication of C12, has C2X (the revision of C that is likely to be published around 10 years from now).

For those of you still scratching their head, the two possibilities are: