The Shape of Code is moving

Derek Jones from The Shape of Code

This blog is moving to a new’ish domain (shape-of-code.com), and hosting company (HostGator). The existing url (shape-of-code.coding-guidelines.com) will continue to work for at least a year, and probably longer.

A beta version of the new site is now running. If things check out (please let me know if you see any issues), https://shape-of-code.com will become the official home next weekend, and the DNS entry for shape-of-code.coding-guidelines.com will be changed to point to the new address.

The existing coding-guidelines.com website has been hosted by PowWeb since June 2005. These days few people will have heard of PowWeb, but in 2005 they often appeared in the list of top hosting sites. I have had a few problems over the years, but I suspect nothing that I would have experienced from other providers. Over time, the functionality provided by PowWeb has decreased, compared to what they used to offer and what others offer today. But since my site usage has been essentially hosting a blog, I have not had a reason to move.

While I have had a nagging feeling I ought to move to a major provider, it was not until a post caused the site to be taken off-line because of a page-views per-hour limit being exceeded, that I decided to move. The limit was exceeded because an article appeared on news.ycombinator and became more popular, more rapidly, than my previous article appearances on ycombinator (which have topped out at 20K+ hits). Customer support were very responsive and quickly reset the page counter, once I contacted them and explained the situation. But why didn’t they inform me (I rarely hear from them, apart from billing, and one false alarm about the site sending spam), and why no option to upgrade?

The screenshot below shows that the daily traffic is around 1K views (mostly from Google searches), with 20k+ daily peak views every few months (sometimes months after the article was posted):

Daily article counts for blog.

Eight months later, the annual fee is due; time for action. HostGator is highly rated by many hosting reviews, and offered site migration (never having migrated a website before, I did not know it was essentially ftp’ing the contents, and maybe some basic WordPress stuff). I signed up.

As you may have guessed, my approach to website maintenance is: If it’s not broken, don’t fix it. This meant the site was running the oldest version of WordPress (4.2.30) and PHP (5.2, which reached end-of-life 10 years ago) that PowWeb supported.

As I learned about website and WordPress migration, I thought: I can do that. My Plan B was to get HostGator to do it.

WordPress migration turned out to be straight forward:

  • export blog contents. WordPress generates an xml file,
  • edit the xml file, replacing all occurrences of shape-of-code.coding-guidelines.com by shape-of-code.com,
  • create WordPress blog on HostGator (to minimise the chance of incompatibilities I stayed with version 4, HostGator offers 4.9.18), selected a few options, and installed a few basic add-ons,
  • ftp directories containing images and code+data to new site,
  • import contents of xml file (there is a 512M limit, my file was 5.5M).

It worked :-)

I was not happy with the theme visually closest to the current blog (Twenty Sixteen), so I tried installing the existing theme (iNove). Despite not being maintained for eight years, it works well enough for me to decide to run with it.

I’m hoping that the new site will run with minimal input from me (apart from writing articles) for the next 10-years.

The Shape of Code is moving

Derek Jones from The Shape of Code

This blog is moving to a new’ish domain (shape-of-code.com), and hosting company (HostGator). The existing url (shape-of-code.coding-guidelines.com) will continue to work for at least a year, and probably longer.

A beta version of the new site is now running. If things check out (please let me know if you see any issues), https://shape-of-code.com will become the official home next weekend, and the DNS entry for shape-of-code.coding-guidelines.com will be changed to point to the new address.

The existing coding-guidelines.com website has been hosted by PowWeb since June 2005. These days few people will have heard of PowWeb, but in 2005 they often appeared in the list of top hosting sites. I have had a few problems over the years, but I suspect nothing that I would have experienced from other providers. Over time, the functionality provided by PowWeb has decreased, compared to what they used to offer and what others offer today. But since my site usage has been essentially hosting a blog, I have not had a reason to move.

While I have had a nagging feeling I ought to move to a major provider, it was not until a post caused the site to be taken off-line because of a page-views per-hour limit being exceeded, that I decided to move. The limit was exceeded because an article appeared on news.ycombinator and became more popular, more rapidly, than my previous article appearances on ycombinator (which have topped out at 20K+ hits). Customer support were very responsive and quickly reset the page counter, once I contacted them and explained the situation. But why didn’t they inform me (I rarely hear from them, apart from billing, and one false alarm about the site sending spam), and why no option to upgrade?

The screenshot below shows that the daily traffic is around 1K views (mostly from Google searches), with 20k+ daily peak views every few months (sometimes months after the article was posted):

Daily article counts for blog.

Eight months later, the annual fee is due; time for action. HostGator is highly rated by many hosting reviews, and offered site migration (never having migrated a website before, I did not know it was essentially ftp’ing the contents, and maybe some basic WordPress stuff). I signed up.

As you may have guessed, my approach to website maintenance is: If it’s not broken, don’t fix it. This meant the site was running the oldest version of WordPress (4.2.30) and PHP (5.2, which reached end-of-life 10 years ago) that PowWeb supported.

As I learned about website and WordPress migration, I thought: I can do that. My Plan B was to get HostGator to do it.

WordPress migration turned out to be straight forward:

  • export blog contents. WordPress generates an xml file,
  • edit the xml file, replacing all occurrences of shape-of-code.coding-guidelines.com by shape-of-code.com,
  • create WordPress blog on HostGator (to minimise the chance of incompatibilities I stayed with version 4, HostGator offers 4.9.18), selected a few options, and installed a few basic add-ons,
  • ftp directories containing images and code+data to new site,
  • import contents of xml file (there is a 512M limit, my file was 5.5M).

It worked 🙂

I was not happy with the theme visually closest to the current blog (Twenty Sixteen), so I tried installing the existing theme (iNove). Despite not being maintained for eight years, it works well enough for me to decide to run with it.

I’m hoping that the new site will run with minimal input from me (apart from writing articles) for the next 10-years.

Mutation testing: its days in the limelight are over

Derek Jones from The Shape of Code

How good a job does a test suite do in detecting coding mistakes in the program it tests?

Mutation testing provides one answer to this question. The idea behind mutation testing is to make a small change to the source code of the program under test (i.e., introduce a coding mistake), and then run the test suite through the mutated program (ideally one or more tests fail, as-in different behavior should be detected); rinse and repeat. The mutation score is the percentage of mutated programs that cause a test failure.

While Mutation testing is 50-years old this year (although the seminal paper/a> did not get published until 1978), the computing resources needed to research it did not start to become widely available until the late 1980s. From then, Until fuzz testing came along, mutation testing was probably the most popular technique studied by testing researchers. A collected bibliography of mutation testing lists 417 papers and 16+ PhD thesis (up to May 2014).

Mutation testing has not been taken up by industry because it tells managers what they already know, i.e., their test suite is not very good at finding coding mistakes.

Researchers concluded that the reason industry had not adopted mutation testing was that it was too resource intensive (i.e., mutate, compile, build, and run tests requires successively more resources). If mutation testing was less resource intensive, then industry would use it (to find out faster what they already knew).

Creating a code mutant is not itself resource intensive, e.g., randomly pick a point in the source and make a random change. However, the mutated source may not compile, or the resulting mutant may be equivalent to one created previously (e.g., the optimised compiled code is identical), or the program takes ages to compile and build; techniques for reducing the build overhead include mutating the compiler intermediate form and mutating the program executable.

Some changes to the source are more likely to be detected by a test suite than others, e.g., replacing <= by > is more likely to be detected than replacing it by < or ==. Various techniques for context dependent mutations have been proposed, e.g., handling of conditionals.

While mutation researchers were being ignored by industry, another group of researchers were listening to industry's problems with testing; automatic test case generation took off. How might different test case generators be compared? Mutation testing offers a means of evaluating the performance of tools arrived on the scene (in practice, many researchers and tool vendors cite statement or block coverage numbers).

Perhaps industry might have to start showing some interest in mutation testing.

A fundamental concern is the extent to which mutation operators modify source in a way that is representative of the kinds of mistakes made by programmers.

The competent programmer hypothesis is often cited, by researchers, as the answer to this question. The hypothesis is that competent programmers write code/programs that is close to correct; the implied conclusion being that mutations, which are small changes, must therefore be like programmer mistakes (the citation often given as the source of this hypothesis discusses data selection during testing, but does mention the term competent programmer).

Until a few years ago, most analysis of fixes of reported faults looked at what coding constructs were involved in correcting the source code, e.g., 296 mistakes in TeX reported by Knuth. This information can be used to generate a probability table for selecting when to mutate one token into another token.

Studies of where the source code was changed, to fix a reported fault, show that existing mutation operators are not representative of a large percentage of existing coding mistakes; for instance, around 60% of 290 source code fixes to AspectJ involved more than one line (mutations usually involve a single line of source {because they operate on single statements and most statements occupy one line}), another study investigating many more fixes found only 10% of fixes involved one line, and similar findings for a study of C, Java, Python, and Haskell (a working link to the data, which is a bit of a mess).

These studies, which investigated the location of all the source code that needs to be changed, to fix a mistake, show that existing mutation operators are not representative of most human coding mistakes. To become representative, mutation operators need to be capable of making coupled changes across multiple lines/functions/methods and even files.

While arguments over the validity of the competent programmer hypothesis rumble on, the need for multi-line changes remains.

Given the lack of any major use-cases for mutation testing, it does not look like it is worth investing lots of resources on this topic. Researchers who have spent a large chunk of their career working on mutation testing will probably argue that you never know what use-cases might crop up in the future. In practice, mutation research will probably fade away because something new and more interesting has come along, i.e., fuzz testing.

There will always be niche use-cases for mutation. For instance, how likely is it that a random change to the source of a formal proof will go unnoticed by its associated proof checker (i.e., the proof checking tool output remains unchanged)?

A study based on mutating the source of Coq verification projects found that 7% of mutations had no impact on the results.

Mutation testing: its days in the limelight are over

Derek Jones from The Shape of Code

How good a job does a test suite do in detecting coding mistakes in the program it tests?

Mutation testing provides one answer to this question. The idea behind mutation testing is to make a small change to the source code of the program under test (i.e., introduce a coding mistake), and then run the test suite through the mutated program (ideally one or more tests fail, as-in different behavior should be detected); rinse and repeat. The mutation score is the percentage of mutated programs that cause a test failure.

While Mutation testing is 50-years old this year (although the seminal paper did not get published until 1978), the computing resources needed to research it did not start to become widely available until the late 1980s. From then, until fuzz testing came along, mutation testing was probably the most popular technique studied by testing researchers. A collected bibliography of mutation testing lists 417 papers and 16+ PhD thesis (up to May 2014).

Mutation testing has not been taken up by industry because it tells managers what they already know, i.e., their test suite is not very good at finding coding mistakes.

Researchers concluded that the reason industry had not adopted mutation testing was that it was too resource intensive (i.e., mutate, compile, build, and run tests requires successively more resources). If mutation testing was less resource intensive, then industry would use it (to find out faster what they already knew).

Creating a code mutant is not itself resource intensive, e.g., randomly pick a point in the source and make a random change. However, the mutated source may not compile, or the resulting mutant may be equivalent to one created previously (e.g., the optimised compiled code is identical), or the program takes ages to compile and build; techniques for reducing the build overhead include mutating the compiler intermediate form and mutating the program executable.

Some changes to the source are more likely to be detected by a test suite than others, e.g., replacing <= by > is more likely to be detected than replacing it by < or ==. Various techniques for context dependent mutations have been proposed, e.g., handling of conditionals.

While mutation researchers were being ignored by industry, another group of researchers were listening to industry's problems with testing; automatic test case generation took off. How might different test case generators be compared? Mutation testing offers a means of evaluating the performance of tools that arrived on the scene (in practice, many researchers and tool vendors cite statement or block coverage numbers).

Perhaps industry might have to start showing some interest in mutation testing.

A fundamental concern is the extent to which mutation operators modify source in a way that is representative of the kinds of mistakes made by programmers.

The competent programmer hypothesis is often cited, by researchers, as the answer to this question. The hypothesis is that competent programmers write code/programs that is close to correct; the implied conclusion being that mutations, which are small changes, must therefore be like programmer mistakes (the citation often given as the source of this hypothesis discusses data selection during testing, but does mention the term competent programmer).

Until a few years ago, most analysis of fixes of reported faults looked at what coding constructs were involved in correcting the source code, e.g., 296 mistakes in TeX reported by Knuth. This information can be used to generate a probability table for selecting when to mutate one token into another token.

Studies of where the source code was changed, to fix a reported fault, show that existing mutation operators are not representative of a large percentage of existing coding mistakes; for instance, around 60% of 290 source code fixes to AspectJ involved more than one line (mutations usually involve a single line of source {because they operate on single statements and most statements occupy one line}), another study investigating many more fixes found only 10% of fixes involved one line, and similar findings for a study of C, Java, Python, and Haskell (a working link to the data, which is a bit disjointed of a mess).

These studies, which investigated the location of all the source code that needs to be changed, to fix a mistake, show that existing mutation operators are not representative of most human coding mistakes. To become representative, mutation operators need to be capable of making coupled changes across multiple lines/functions/methods and even files.

While arguments over the validity of the competent programmer hypothesis rumble on, the need for multi-line changes remains.

Given the lack of any major use-cases for mutation testing, it does not look like it is worth investing lots of resources on this topic. Researchers who have spent a large chunk of their career working on mutation testing will probably argue that you never know what use-cases might crop up in the future. In practice, mutation research will probably fade away because something new and more interesting has come along, i.e., fuzz testing.

There will always be niche use-cases for mutation. For instance, how likely is it that a random change to the source of a formal proof will go unnoticed by its associated proof checker (i.e., the proof checking tool output remains unchanged)?

A study based on mutating the source of Coq verification projects found that 7% of mutations had no impact on the results.

Testing rounded data for a circular uniform distribution

Derek Jones from The Shape of Code

Circular statistics deals with analysis of measurements made using a circular scale, e.g., minutes past the hour, days of the week. Wikipedia uses the term directional statistics, the traditional use being measurements of angles, e.g., wind direction.

Package support for circular statistics is rather thin on the ground. R’s circular package is one of the best, and the book “Circular Statistics in R” provides the only best introduction to the subject.

Circular statistics has a few surprises for those new to the subject (apart from a few name changes, e.g., the von Mises distribution is effectively the ‘circular Normal distribution’), including:

  • the mean value contains two components, a direction and a length, e.g., mean wind direction and strength,
  • there are several definitions of variance, with angular variance having a value between 0 and 2, and circular variance having a value between 0 and 1. The circular standard deviation is not the square root of variance, but rather: sqrt{-2 log R}, where R is the mean length.

The basic techniques used in circular statistics are still relatively new, compared to the more well known basic statistical techniques. For instance, it was recently discovered that having more measurements may reduce the reliability of the Rao spacing test (used to test whether a sample has a uniform circular distribution); generally, having more measurements improves the reliability of a statistical test.

The plot below shows Rose diagrams for the number of commits in each 3-hour period of a day for Linux and FreeBSD (mean direction and length in green; code+data):

Project actual/estimate ratio against percent complete.

The Linux kernel source has far fewer commits at the weekend, compared to working days. Given the number of people whose job is to work on the Linux kernel, compared to the number of people doing it out of interest, this difference is not surprising. The percentage of people working on OpenBSD as a job is small, and there does not appear to be a big difference between weekends and workdays. There is a lot of variation in the number of commits during each 3-hour period of a day, but the number of commits per day does not vary so much; the number of OpenBSD commits per day of week is:

            Mon   Tue   Wed   Thu   Fri   Sat   Sun 
          26909 26144 25705 25104 24765 22812 24304 

Does this distribution of commits per day have a uniform distribution (to some confidence level)?

Like all measurements, those made on a circular scale are rounded to some number of digits. Measurements may also be rounded, or binned, to particular units of the scale, e.g., measured to the nearest degree, or nearest minute.

A recent paper, by Landler, Ruxton and Malkemper, found that for samples containing around five hundred or more measurements, rounding to the nearest degree was sufficient to cause the Rao spacing test to almost always report non-uniformity, i.e., for non-trivial samples the rounding was sufficient to cause the test to detect non-uniformity (things worked as expected for samples containing fewer than 100 measurements).

Landler et al found that adding a small amount of noise (drawn from a von Mises distribution) to the rounded measurements appeared to ‘fix’ the incorrect behavior, i.e., rejecting the hypothesis of a uniform distribution, when a uniform distribution may be present.

The rao.spacing.test function, in the circular package, rejected that null hypothesis that the OpenBSD daily data has a uniform distribution. However, when noise is added to each day value (i.e., adding a random fraction to the day values, using rvonmises(length(c_per_day), circular(0), 2.0)), the call to rao.spacing.test failed to reject the null hypothesis of uniformity at the 0.05 level (i.e., the daily distribution is probably uniform).

How many research results are affected by this discovery?

I very rarely encounter the use of circular statistics (even though they should probably have been used in places), but then I spend my time reading software engineering papers, whose use of statistics tends to be primitive. I plan to include a brief mention of the use of the Rao spacing test with binned data in the addendum to my Evidence-based software engineering book (which includes the above example).

Testing rounded data for a circular uniform distribution

Derek Jones from The Shape of Code

Circular statistics deals with analysis of measurements made using a circular scale, e.g., minutes past the hour, days of the week. Wikipedia uses the term directional statistics, the traditional use being measurements of angles, e.g., wind direction.

Package support for circular statistics is rather thin on the ground. R’s circular package is one of the best, and the book “Circular Statistics in R” provides the only best introduction to the subject.

Circular statistics has a few surprises for those new to the subject (apart from a few name changes, e.g., the von Mises distribution is effectively the ‘circular Normal distribution’), including:

  • the mean value contains two components, a direction and a length, e.g., mean wind direction and strength,
  • there are several definitions of variance, with angular variance having a value between 0 and 2, and circular variance having a value between 0 and 1. The circular standard deviation is not the square root of variance, but rather: sqrt{-2 log R}, where R is the mean length.

The basic techniques used in circular statistics are still relatively new, compared to the more well known basic statistical techniques. For instance, it was recently discovered that having more measurements may reduce the reliability of the Rao spacing test (used to test whether a sample has a uniform circular distribution); generally, having more measurements improves the reliability of a statistical test.

The plot below shows Rose diagrams for the number of commits in each 3-hour period of a day for Linux and FreeBSD (mean direction and length in green; code+data):

Project actual/estimate ratio against percent complete.

The Linux kernel source has far fewer commits at the weekend, compared to working days. Given the number of people whose job is to work on the Linux kernel, compared to the number of people doing it out of interest, this difference is not surprising. The percentage of people working on OpenBSD as a job is small, and there does not appear to be a big difference between weekends and workdays. There is a lot of variation in the number of commits during each 3-hour period of a day, but the number of commits per day does not vary so much; the number of OpenBSD commits per day of week is:

            Mon   Tue   Wed   Thu   Fri   Sat   Sun 
          26909 26144 25705 25104 24765 22812 24304 

Does this distribution of commits per day have a uniform distribution (to some confidence level)?

Like all measurements, those made on a circular scale are rounded to some number of digits. Measurements may also be rounded, or binned, to particular units of the scale, e.g., measured to the nearest degree, or nearest minute.

A recent paper, by Landler, Ruxton and Malkemper, found that for samples containing around five hundred or more measurements, rounding to the nearest degree was sufficient to cause the Rao spacing test to almost always report non-uniformity, i.e., for non-trivial samples the rounding was sufficient to cause the test to detect non-uniformity (things worked as expected for samples containing fewer than 100 measurements).

Landler et al found that adding a small amount of noise (drawn from a von Mises distribution) to the rounded measurements appeared to ‘fix’ the incorrect behavior, i.e., rejecting the hypothesis of a uniform distribution, when a uniform distribution may be present.

The rao.spacing.test function, in the circular package, rejected that null hypothesis that the OpenBSD daily data has a uniform distribution. However, when noise is added to each day value (i.e., adding a random fraction to the day values, using rvonmises(length(c_per_day), circular(0), 2.0), although runif(length(c_per_day)) is probably more appropriate {and produces essentially the same result}), the call to rao.spacing.test failed to reject the null hypothesis of uniformity at the 0.05 level (i.e., the daily distribution is probably uniform).

How many research results are affected by this discovery?

I very rarely encounter the use of circular statistics (even though they should probably have been used in places), but then I spend my time reading software engineering papers, whose use of statistics tends to be primitive. I plan to include a brief mention of the use of the Rao spacing test with binned data in the addendum to my Evidence-based software engineering book (which includes the above example).

Multiple estimates for the same project

Derek Jones from The Shape of Code

The first question I ask, whenever somebody tells me that a project was delivered on schedule (or within budget), is which schedule (or budget)?

New schedules are produced for projects that are behind schedule, and costs get re-estimated.

What patterns of behavior might be expected to appear in a project’s reschedulings?

It is to be expected that as a project progresses, subsequent schedules become successively more accurate (in the sense of having a completion date and cost that is closer to the final values). The term cone of uncertainty is sometimes applied as a visual metaphor in project management, with the schedule becoming less uncertain as the project progresses.

The only publicly available software project rescheduling data, from Landmark Graphics, is for completed projects, i.e., cancelled projects are not included (121 completed projects and 882 estimates).

The traditional project management slide has some accuracy metric improving as work on a project approaches completion. The plot below shows the percentage of a project completed when each estimate is made, against the ratio Actual/Estimate; the y-axis uses a log scale so that under/over estimates appear symmetrical (code+data):

Project actual/estimate ratio against percent complete.

The closer a point to the blue line, the more accurate the estimate. The red line shows maximum underestimation, i.e., estimating that the project is complete when there is still more work to be done. A new estimate must be greater than (or equal) to the work already done, i.e., Work_{done} <= Estimate, and Work_{done} = Actual*Percentage_{complete}.

Rearranging, we get: Actual/Estimate <= 1/Percentage_{complete} (plotted in red). The top of the ‘cone’ does not represent managements’ increasing certainty, with project progress, it represents the mathematical upper bound on the possible inaccuracy of an estimate.

In theory there is no limit on overestimating (i.e., points appearing below the blue line), but in practice management are under pressure to deliver as early as possible and to minimise costs. If management believe they have overestimated, they have an incentive to hang onto the time/money allocated (the future is uncertain).

Why does management invest time creating a new schedule?

If information about schedule slippage leaks out, project management looks bad, which creates an incentive to delay rescheduling for as long as possible (i.e., let’s pretend everything will turn out as planned). The Landmark Graphics data comes from an environment where management made weekly reports and estimates were updated whenever the core teams reached consensus (project average was eight times).

The longer a project is being worked on, the greater the opportunity for more unknowns to be discovered and the schedule to slip, i.e., longer projects are expected to acquire more re-estimates. The plot below shows the number of estimates made, for each project, against the initial estimated duration (red/green) and the actual duration (blue/purple); lines are loess fits (code+data):

Number of estimates against project initial estimated and actual duration.

What might be learned from any patterns appearing in this data?

When presented with data on the sequence of project estimates, my questions revolve around the reasons for spending time creating a new estimate, and the amount of time spent on the estimate.

A lot of time may have been invested in the original estimate, but how much time is invested in subsequent estimates? Are later estimates simply calculated as a percentage increase, a politically acceptable value (to the stakeholder funding for the project), or do they take into account what has been learned so far?

The information needed to answer these answers is not present in the data provided.

However, this evidence of the consistent provision of multiple project estimates drives another nail in to the coffin of estimation research based on project totals (e.g., if data on project estimates is provided, one estimate per project, were all estimates made during the same phase of the project?)

Multiple estimates for the same project

Derek Jones from The Shape of Code

The first question I ask, whenever somebody tells me that a project was delivered on schedule (or within budget), is which schedule (or budget)?

New schedules are produced for projects that are behind schedule, and costs get re-estimated.

What patterns of behavior might be expected to appear in a project’s reschedulings?

It is to be expected that as a project progresses, subsequent schedules become successively more accurate (in the sense of having a completion date and cost that is closer to the final values). The term cone of uncertainty is sometimes applied as a visual metaphor in project management, with the schedule becoming less uncertain as the project progresses.

The only publicly available software project rescheduling data, from Landmark Graphics, is for completed projects, i.e., cancelled projects are not included (121 completed projects and 882 estimates).

The traditional project management slide has some accuracy metric improving as work on a project approaches completion. The plot below shows the percentage of a project completed when each estimate is made, against the ratio Actual/Estimate; the y-axis uses a log scale so that under/over estimates appear symmetrical (code+data):

Project actual/estimate ratio against percent complete.

The closer a point to the blue line, the more accurate the estimate. The red line shows maximum underestimation, i.e., estimating that the project is complete when there is still more work to be done. A new estimate must be greater than (or equal) to the work already done, i.e., Work_{done} <= Estimate, and Work_{done} = Actual*Percentage_{complete}.

Rearranging, we get: Actual/Estimate <= 1/Percentage_{complete} (plotted in red). The top of the ‘cone’ does not represent managements’ increasing certainty, with project progress, it represents the mathematical upper bound on the possible inaccuracy of an estimate.

In theory there is no limit on overestimating (i.e., points appearing below the blue line), but in practice management are under pressure to deliver as early as possible and to minimise costs. If management believe they have overestimated, they have an incentive to hang onto the time/money allocated (the future is uncertain).

Why does management invest time creating a new schedule?

If information about schedule slippage leaks out, project management looks bad, which creates an incentive to delay rescheduling for as long as possible (i.e., let’s pretend everything will turn out as planned). The Landmark Graphics data comes from an environment where management made weekly reports and estimates were updated whenever the core teams reached consensus (project average was eight times).

The longer a project is being worked on, the greater the opportunity for more unknowns to be discovered and the schedule to slip, i.e., longer projects are expected to acquire more re-estimates. The plot below shows the number of estimates made, for each project, against the initial estimated duration (red/green) and the actual duration (blue/purple); lines are loess fits (code+data):

Number of estimates against project initial estimated and actual duration.

What might be learned from any patterns appearing in this data?

When presented with data on the sequence of project estimates, my questions revolve around the reasons for spending time creating a new estimate, and the amount of time spent on the estimate.

A lot of time may have been invested in the original estimate, but how much time is invested in subsequent estimates? Are later estimates simply calculated as a percentage increase, a politically acceptable value (to the stakeholder funding for the project), or do they take into account what has been learned so far?

The information needed to answer these answers is not present in the data provided.

However, this evidence of the consistent provision of multiple project estimates drives another nail in to the coffin of estimation research based on project totals (e.g., if data on project estimates is provided, one estimate per project, were all estimates made during the same phase of the project?)

Readability: a scientific approach

Derek Jones from The Shape of Code

Readability, as applied to software development today, is a meaningless marketing term. Readability is promoted as a desirable attribute, and is commonly claimed for favored programming languages, particular styles of programming, or ways of laying out source code.

Whenever somebody I’m talking to, or listening to in a talk, makes a readability claim, I ask what they mean by readability, and how they measured it. The speaker invariably fumbles around for something to say, with some dodging and weaving before admitting that they have not measured readability. There have been a few studies that asked students to rate the readability of source code (no guidance was given about what readability might be).

If somebody wanted to investigate readability from a scientific perspective, how might they go about it?

The best way to make immediate progress is to build on what is already known. There has been over a century of research on eye movement during reading, and two model of eye movement now dominate, i.e., the E-Z Reader model and SWIFT model. Using eye-tracking to study developers is slowly starting to be adopted by researchers.

Our eyes don’t smoothly scan the world in front of us, rather they jump from point to point (these jumps are known as a saccade), remaining fixed long enough to acquire information and calculate where to jump next. The image below is an example from an eye tracking study, where subjects were asking to read a sentence (see figure 770.11). Each red dot appears below the center of each saccade, and the numbers show the fixation time (in milliseconds) for that point (code):

Saccade points in a sentence, and fixation times.

Models of reading are judged by the accuracy of their predictions of saccade landing points (within a given line of text), and fixation time between saccades. Simulators implementing the E-Z Reader and SWIFT models have found that these models have comparable performance, and the robustness of these models are compared by looking at the predictions they make about saccade behavior when reading what might be called unconventional material, e.g., mirrored or scarmbeld text.

What is the connection between the saccades made by readers and their understanding of what they are reading?

Studies have found that fixation duration increases with text difficulty (it is also affected by decreases with word frequency and word predictability).

It has been said that attention is the window through which we perceive the world, and our attention directs what we look at.

A recent study of the SWIFT model found that its predictions of saccade behavior, when reading mirrored or inverted text, agreed well with subject behavior.

I wonder what behavior SWIFT would predict for developers reading a line of code where the identifiers were written in camelCase or using underscores (sometimes known as snake_case)?

If the SWIFT predictions agreed with developer saccade behavior, a raft of further ‘readability’ tests spring to mind. If the SWIFT predictions did not agree with developer behavior, how might the model be updated to support the reading of lines of code?

Until recently, the few researchers using eye tracking to investigate software engineering behavior seemed to be having fun playing with their new toys. Things are starting to settle down, with some researchers starting to pay attention to existing models of reading.

What do I predict will be discovered?

Lots of studies have found that given enough practice, people can become proficient at handling some apparently incomprehensible text layouts. I predict that given enough practice, developers can become equally proficient at most of the code layout schemes that have been proposed.

The important question concerning text layout, is: which one enables an acceptable performance from a wide variety of developers who have had little exposure to it? I suspect the answer will be the one that is closest to the layout they have had the most experience,i.e., prose text.

Readability: a scientific approach

Derek Jones from The Shape of Code

Readability, as applied to software development today, is a meaningless marketing term. Readability is promoted as a desirable attribute, and is commonly claimed for favored programming languages, particular styles of programming, or ways of laying out source code.

Whenever somebody I’m talking to, or listening to in a talk, makes a readability claim, I ask what they mean by readability, and how they measured it. The speaker invariably fumbles around for something to say, with some dodging and weaving before admitting that they have not measured readability. There have been a few studies that asked students to rate the readability of source code (no guidance was given about what readability might be).

If somebody wanted to investigate readability from a scientific perspective, how might they go about it?

The best way to make immediate progress is to build on what is already known. There has been over a century of research on eye movement during reading, and two model of eye movement now dominate, i.e., the E-Z Reader model and SWIFT model. Using eye-tracking to study developers is slowly starting to be adopted by researchers.

Our eyes don’t smoothly scan the world in front of us, rather they jump from point to point (these jumps are known as a saccade), remaining fixed long enough to acquire information and calculate where to jump next. The image below is an example from an eye tracking study, where subjects were asking to read a sentence (see figure 770.11). Each red dot appears below the center of each saccade, and the numbers show the fixation time (in milliseconds) for that point (code):

Saccade points in a sentence, and fixation times.

Models of reading are judged by the accuracy of their predictions of saccade landing points (within a given line of text), and fixation time between saccades. Simulators implementing the E-Z Reader and SWIFT models have found that these models have comparable performance, and the robustness of these models are compared by looking at the predictions they make about saccade behavior when reading what might be called unconventional material, e.g., mirrored or scarmbeld text.

What is the connection between the saccades made by readers and their understanding of what they are reading?

Studies have found that fixation duration increases with text difficulty (it is also affected by decreases with word frequency and word predictability).

It has been said that attention is the window through which we perceive the world, and our attention directs what we look at.

A recent study of the SWIFT model found that its predictions of saccade behavior, when reading mirrored or inverted text, agreed well with subject behavior.

I wonder what behavior SWIFT would predict for developers reading a line of code where the identifiers were written in camelCase or using underscores (sometimes known as snake_case)?

If the SWIFT predictions agreed with developer saccade behavior, a raft of further ‘readability’ tests spring to mind. If the SWIFT predictions did not agree with developer behavior, how might the model be updated to support the reading of lines of code?

Until recently, the few researchers using eye tracking to investigate software engineering behavior seemed to be having fun playing with their new toys. Things are starting to settle down, with some researchers starting to pay attention to existing models of reading.

What do I predict will be discovered?

Lots of studies have found that given enough practice, people can become proficient at handling some apparently incomprehensible text layouts. I predict that given enough practice, developers can become equally proficient at most of the code layout schemes that have been proposed.

The important question concerning text layout, is: which one enables an acceptable performance from a wide variety of developers who have had little exposure to it? I suspect the answer will be the one that is closest to the layout they have had the most experience,i.e., prose text.