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Why is Cobol still popular in Japan?
Rummaging around the web for empirical software engineering data, I found a survey of programming language usage in Japan. This survey (based on 505 projects in 24 companies) has Cobol in the number two slot for 2012, a bit higher than I would have expected (it very rarely appears at all in US/UK ‘popularity’ lists):
Language Projects Java 822 28.2% COBOL 464 15.9% VB 371 12.7% C 326 11.2% Other languages 208 7.1% C++ 189 6.5% Visual Basic.NET 136 4.7% Visual C++ 105 3.6% C# 101 3.5% PL/SQL 57 2.0% Pro*C 23 0.8% Excel（VBA） 18 0.6% Developer2000 17 0.6% ABAP 15 0.5% HTML 14 0.5% Delphi 11 0.4% PL/I 10 0.3% Perl 10 0.3% PowerBuilder 7 0.2% Shell 7 0.2% XML 6 0.2%
A quick overview of Cobol for those readers who have never encountered it.
Cobol is a domain specific language ideally suited for business data processing in the 1960/70/80/90s. During this period computer memory was often measured in kilobytes, data came in an unbelievably wide range of different formats, operations on data mostly involved sorting and basic arithmetic, and output data format was/is very important. By “unbelievably wide range” think of lots of point-of-sale vendors deciding how their devices would write data to punch cards/paper tape/magnetic tape, just handling the different encodings that have been used for the plus/minus sign can make the head spin; combine the requirement that programs handle different data formats with tiny computer memory capacity, and you get data structure overlays that make C programmers look like rank amateurs, all the real action in Cobol programs occurs in the DATA DIVISION.
So where are we today? Companies use computers to solve a wider range of problems don’t they (so even if Cobol usage stayed the same its percentage usage should be low)? If point-of-sale terminals still produce a wide range of weird and wonderful data formats, isn’t it easy enough to write the appropriate libraries to convert (and we have much more storage these days)?
Why might Cobol still be so popular in Japan (and perhaps elsewhere, if anybody over 25 was included in the survey)? Some ideas:
- Cobol is still the best language to use for business data processing,
- the sample is not representative of the Japanese software development industry. As a government body perhaps the Information-Technology Promotion Agency primarily deals with large well established companies; the data came from a relatively small number of companies (i.e., 24),
- the Japanese are known for being conservative and maintaining traditions. Change is almost considered a necessity here in the West, this has led to the use of way too many programming languages in industry (I have previously written about what a mistake it is to invent a new language).
Break even ratios for development investment decisions
Developers are constantly being told that it is worth making the effort when writing code to make it maintainable (whatever that might be). Looking at this effort as an investment what kind of return has to be achieved to make it worthwhile?
Short answer: The percentage saving during maintenance has to be twice as great as the percentage investment during development to break even, higher ratio to do better.
The longer answer is below as another draft section from my book Empirical software engineering with R book. As always comments and pointers to more data welcome. R code and data here.
Break even ratios for development investment decisions
Upfront investments are often made during software development with the aim of achieving benefits later (e.g., reduced cost or time). Examples of such investments include spending time planning, designing or commenting the code. The following analysis calculates the benefit that must be achieved by an investment for that investment to break even.
While the analysis uses years as the unit of time it is not unit specific and with suitable scaling months, weeks, hours, etc can be used. Also the unit of development is taken to be a complete software system, but could equally well be a subsystem or even a function written by one person.
Let 
be the original development cost and 
the yearly maintenance costs, we start by keeping things simple and assume is the same for every year of maintenance; the total cost of the system over 
years is:
If we make an investment of 
% in reducing future maintenance costs with the expectations of achieving a benefit of 
%, the total cost becomes:
and for the investment to break even the following inequality must hold:
expanding and simplifying we get:
or:
If the inequality is true the ratio 
is the primary contributor to the right-hand-side and must be greater than 1.
A significant problem with the above analysis is that it does not take into account a major cost factor; many systems are replaced after a surprisingly short period of time. What relationship does the ratio need to have when system survival rate is taken into account?
Let 
be the percentage of systems that survive each year, total system cost is now:
where 
Summing the power series for the maximum of years that any system in a company’s software portfolio survives gives:
and the break even inequality becomes:
The development/maintenance ratio is now based on the yearly cost multiplied by a factor that depends on the system survival rate, not the total maintenance cost
If we take >= 5 and a survival rate of less than 60% the inequality simplifies to very close to:
telling us that if the yearly maintenance cost is equal to the development cost (a situation more akin to continuous development than maintenance and seen in 5% of systems in the IBM dataset below) then savings need to be at least twice as great as the investment for that investment to break even. Taking the mean of the IBM dataset and assuming maintenance costs spread equally over the 5 years, a break even investment requires savings to be six times greater than the investment (for a 60% survival rate).
The plot below gives the minimum required saving/investment ratio that must be achieved for various system survival rates (black 0.9, red 0.8, blue 0.7 and green 0.6) and development/yearly maintenance cost ratios; the line bundles are for system lifetimes of 5.5, 6, 6.5, 7 and 7.5 years (ordered top to bottom)
Figure 1. Break even saving/investment ratio for various system survival rates (black 0.9, red 0.8, blue 0.7 and green 0.6) and development/maintenance ratios; system lifetimes are 5.5, 6, 6.5, 7 and 7.5 years (ordered top to bottom)
Development and maintenance costs
Dunn’s PhD thesis <book Dunn_11> lists development and total maintenance costs (for the first five years) of 158 software systems from IBM. The systems varied in size from 34 to 44,070 man hours of development effort and from 21 to 78,121 man hours of maintenance.
The plot below shows the ratio of development to five year maintenance costs for the 158 software systems. The mean value is around one and if we assume equal spending during the maintenance period then 
.
Figure 2. Ratio of development to five year maintenance costs for 158 IBM software systems sorted in size order. Data from Dunn <book Dunn_11>.
The best fitting common distribution for the maintenance/development ratio is the <Beta distribution>, a distribution often encountered in project planning.
Is there a correlation between development man hours and the maintenance/development ratio (e.g., do smaller systems tend to have a lower/higher ratio)? A Spearman rank correlation test between the maintenance/development ratio and development man hours gives:
|
showing very little connection between the two values.
Is the data believable?
While a single company dataset might be thought to be internally consistent in its measurement process, IBM is a very large company and it is possible that the measurement processes used were different.
The maintenance data applies to software systems that have not yet reached the end of their lifespan and is not broken down by year. Any estimate of total or yearly maintenance can only be based on assumptions or lifespan data from other studies.
System lifetime
A study by Tamai and Torimitsu <book Tamai_92> obtained data on the lifespan of 95 software systems. The plot below shows the number of systems surviving for at least a given number of years and a fit of an <Exponential distribution> to the data.
Figure 3. Number of software systems surviving to a given number of years (red) and an exponential fit (black, data from Tamai <book Tamai_92>).
The nls function gives 
as the best fit, giving a half-life of 5.4 years (time for the number of systems to reduce by 50%), while rounding to 
gives a half-life of 6.6 years and reducing to 
a half life of 4.6 years.
It is worrying that such a small change to the estimated fit can have such a dramatic impact on estimated half-life, especially given the uncertainty in the applicability of the 20 year old data to today’s environment. However, the saving/investment ratio plot above shows that the final calculated value is not overly sensitive to number of years.
Is the data believable?
The data came from a questionnaire sent to the information systems division of corporations using mainframes in Japan during 1991.
It could be argued that things have stabilised over the last 20 years ago and complete software replacements are rare with most being updated over longer periods, or that growing customer demands is driving more frequent complete system replacement.
It could be argued that large companies have larger budgets than smaller companies and so have the ability to change more quickly, or that larger companies are intrinsically slower to change than smaller companies.
Given the age of the data and the application environment it came from a reasonably wide margin of uncertainty must be assigned to any usage patterns extracted.
Summary
Based on the available data an investment during development must recoup a benefit during maintenance that is at least twice as great in percentage terms to break even:
- systems with a yearly survival rate of less than 90% must have a benefit/investment rate greater than two if they are to break even,
- systems with a development/yearly maintenance rate of greater than 20% must have a benefit/investment rate greater than two if they are to break even.
The availanble software system replacement data is not reliable enough to suggest any more than that the estimated half-life might be between 4 and 8 years.
This analysis only considers systems that have been delivered and started to be used. Projects are cancelled before reaching this stage and including these in the analysis would increase the benefit/investment break even ratio.
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