Martin Fowler’s Design Stamina Hypothesis expresses a widely held belief among practicing software engineers and other technical professionals that is also taught in computer science curricula. Basically, the idea is that “good software design,” a vaguely defined concept, fairly quickly pays for itself through faster, better, cheaper software development in the long run.
Martin Fowler, Chief Scientist for ThoughtWorks and a noted writer on agile software development, software design and refactoring, encapsulates this concept in this “pseudo-graph”:
The remarkable thing about this graph is that it is based on no data as Martin Fowler candidly admits in his blog post and presentations (see for example the third mini-talk, about 45:00, in Software Development in the 21st Century by Martin Fowler). Yes, that is right: no data. 🙂 It is a hypothesis, a conjecture, but one held by Martin Fowler and strongly, even fanatically held by many software engineers and other technical professionals.
It is hard to define the terms in the design stamina hypothesis. In particular, what is “good design?” This often refers to a beautiful, modular system of software that is allegedly “scalable and maintainable”. Also the modules are allegedly reusable. I have certainly had the experience of trying to work with modular software that was neither scalable nor maintainable nor reusable and yet seemed to follow the common tenets of “good design.”
The hypothesis also sets up a straw man. True “no design” is actually pretty rare in professional software development. Rather the real debates are between “good design” (my design) and “less good design” (your design, also known as [email protected]#$%). Or between “more time spent on design” (product ship date is one year away) and “less time spent on design” (product ship date is two weeks away).
Martin Fowler begs off on producing actual data to back up his pseudo-graph. In highly technical, highly mathematical areas of software development, it is often possible to define objective performance metrics that correspond closely to the business value of the products or services.
In speech recognition a good objective performance metric is the word recognition accuracy of the speech recognition engine; a speech recognition engine that recognizes ninety-five percent of spoken words is better than one that recognizes ninety percent.
In video compression, one of the key objective performance metrics is the compression ratio which is simply the size of the video before it is compressed divided by the size of the video after it is compressed. This translates directly into lower storage costs, more channels of video for a cable system or YouTube, and so on. It is not hard to relate it directly to the dollar business value that financial analysts (bean-counters) care about.
Here is a graph of the compression ratio, the performance, of the best video compression technologies in the world versus time:
Video compression improved very little between 1995 and 2003. This was actually a period of wide-open competition in video codecs (codec stands for encoder/decoder or compressor/decompressor) because Microsoft, despite its reputation, provided an open architecture through Video for Windows and MCI (Media Control Interface) that enabled third party developers to rapidly integrate any video or audio compression algorithm into the then universal Windows operating system. In fact, hundreds of video codecs proliferated during this period. But the bit rate for minimum usable video remained stuck at about 1 Megabit per second.
Suddenly, video compression leaped forward during 2003, in just a matter of months. The new advances were quickly copied by many video codecs. The bit rate for minimum usable video dropped from one megabit per second to around 275 kilobits per second — lower for some “talking heads” video that is easier to compress.
This dramatic technical advance remains largely unnoticed by the general public! It in fact enabled YouTube, Skype, and the proliferation of video on the Internet since 2003.
Then, the compression ratio went flat again. In fact, there was negligible progress until 2008. The early “high performance” video codecs such as H.264/AVC (Advanced Video Coding) had some problems properly reproducing skin tone, which is noticeable since people generally look at faces. In my graph, I use a different color from 2008 onwards to show the improvement in skin tone and perceived quality although the compression ratio did not change significantly.
What does this tell us about the design stamina hypothesis? Were the video codecs the product of “no design” from 1995 (actually earlier) to 2003? Did they suddenly switch over to “good software design” for a few brief months in 2003? Then the crazed cowboy coders took over again in 2004, inflicting “no design” until a brief shining moment in 2008 when the agile software designers took over again before being ousted in a violent coup by the cowboy coders?
Clearly, the actual performance curves bear little resemblance to the beautiful “good design” and “no design” curves in the design stamina hypothesis pseudo-graph. In fact, they resemble the famous “technology S-curve” postulated by students of the history of technology, invention and discovery.
The basic idea behind the Technology S Curve is that technologies tend to go through a period of slow development during their early stages, a period of rapid development when the new technology gets past the proof of concept stage, and then slow down and often plateau when technical limits, often from fundamental physics or mathematics are encountered.
In aviation, propeller planes eventually topped out in speed. Jets were needed to go faster, break the sound barrier. Chemical rockets are faster but top out at several miles per second due to the constraints of the rocket equation and known materials. In principal, nuclear rockets could go faster. Fusion propulsion even faster. Antimatter rockets might be able to reach near the speed of light and travel to the nearest stars.
NOTE: Above graph added to post on July 18, 2014 — after first publication. The data is the flight airspeed record data from Wikipedia (accessed on July 18, 2014). See the appendix for the GNU Octave Code and cleaned data from the Wikipedia page used to generate the graph. The sharp climb in the 1950’s is due to the introduction of jet engines. Note also that the top speed of propeller planes is roughly linear with year — not an idealized S-curve. The final top speed record is for the SR-71 Blackbird spy plane — still officially the top record speed for a jet aircraft.
Each technology plateaus at some point and something new, sometimes a new component, sometimes a radical new architecture is needed. This gives rise to the technology S curve in many cases — not in all.
Heavily mathematical algorithms and software, like video compression, often seem to behave like this. Progress occurs in fits and starts, periods of no progress and sudden jumps, occasional periods of steady incremental progress. It often does not resemble the curves in the design stamina hypothesis pseudo-graph.
Leprechauns in the Measurement Free Zone
Software engineering and software design is a remarkably evidence-free field. One researcher has described it as “The Measurement Free Zone.” This is all the more remarkable given the high intelligence and technical backgrounds of the software design theorists and practitioners.
A few years ago Agile software development enthusiast Laurent Bossavit wrote an online book The Leprechauns of Software Engineering: How folklore turns into fact and what to do about it detailing his research into the basis for a number of common, heavily cited beliefs in software engineering, beliefs which he had held. He has also written an article on his experience for Model View Culture web site: The Making of Myths. The beliefs often turn out to be based on very limited evidence, open to alternative interpretation, or even pseudo-graphs like Fowler’s Design Stamina Hypothesis that illustrate not data but simply a personal belief, perhaps based on some undocumented personal experience.
Undocumented personal experience is also known as “anecdotal evidence” and anathema, with some justification, in the mainstream scientific and professional engineering literature. I don’t entirely agree with this mainstream taboo, but one should certainly be cautious with “anecdotal evidence.”
When I investigated the epidemic of autism in the United States (see The Mathematics of Autism), I found many accounts by parents of autism or at least behavioral problems diagnosed as autism occurring in conjunction with vaccinations. These are often very specific. My kid received the MMR (Measles-Mumps-Rubella) vaccine at about 18 months, had a reaction to the vaccine, and then stopped speaking and began to exhibit odd behavior leading to a diagnosis of autism. These are direct, specific personal experience and many parents are quite certain that the vaccines somehow caused the autism.
The “you read Andrew Wakefield’s articles and are just imagining it after the fact” explanations by the CDC and medical-scientific establishment, adamantly and financially committed to vaccines, aren’t particularly convincing or credible. But is it true? Do vaccines cause autism or is there some other explanation for these experiences?
In the technology S-curve, if you happen to be involved in a project during the middle rapid-progress period, it will look exactly like Martin Fowler’s “good design” curve. On the other hand, if you are involved later in the project, starting near or after the end of the rapid progress period, it will look exactly like the “no design” curve.
Often as technologies reach the plateau, they become very complicated. This complexity however buys very small or no improvements in performance. The technology is simply reaching its limits and it takes an awful lot to squeeze a little more out of it. At this point, a technology that is becoming complicated in this way may genuinely resembles “no design,” spaghetti code, inexplicably complicated to a newcomer.
In fact, a high performance video codec like the free open-source x264 is extremely complex.
Joel Spolsky wrote a widely-read, widely ignored blog post Things You Should Never Do about the bizarre and often disastrous tendency of software engineers to try to rewrite shipping, successful software — from scratch in many cases. Software marketing expert Merrill R. (Rick) Chapman describes several cases of this at companies he worked for in the 1980’s in his book In Search of Stupidity: Over Twenty Years of High Tech Marketing Disasters. Not infrequently the attempt to rewrite the “bad code” takes an extremely long time or fails outright, by which time a competitor has overtaken the company with new features in a competing product that was not rewritten or refactored in modern parlance.
In most of these cases, the rewriters or refactorers encounter an extremely complex confusing code base presumably written by highly paid professional software developers who have either cashed in their stock options and are now playing golf in Maui or have been downsized without reward by their heartless employer in favor of younger, presumably smarter developers trained in the latest software design methodology. 🙂 The obvious conclusion is that the working software was built with “no design.” Could Martin Fowler and the Design Stamina Hypothesis be wrong?
A Call for Data
The Design Stamina Hypothesis is admittedly not based on data. It is a hypothesis, a conjecture. Martin Fowler clearly admits this — to his credit. Martin Fowler didn’t really invent this concept. I have heard some variant of it for over twenty years (the blog post is dated 2007) especially from advocates of various software design methodologies (structured design in the 1980’s, object-oriented design in the 1990’s, Agile and Lean and XP and so on in the 00’s).
Where is the data?
It is possible to construct objective performance metrics like the compression ratio that correspond closely to business value, certainly in highly technical, mathematical software like video compression or speech recognition.
There are probably similar objective performance metrics in business software. For example, the number of transactions per second that a business software system — payroll, order entry, etc. — can process. These can be plotted against time and effort. One can certainly measure roughly the amount of time spent on design versus coding, testing, or other activities. Does the data actually show the curves in the Design Stamina Hypothesis, technology S-curves, something else, or a lot of confusion?
The benefits of such evidence-based decision making may well include avoiding making the expensive and often fatal mistake of attempting to rewrite or refactor an extremely complex product or system that is extremely complex for good reasons such as the plateau at the end of the technology S-curve.
© 2014 John F. McGowan
About the Author
John F. McGowan, Ph.D. solves problems using mathematics and mathematical software, including developing video compression and speech recognition technologies. He has extensive experience developing software in C, C++, Visual Basic, Mathematica, MATLAB, and many other programming languages. He is probably best known for his AVI Overview, an Internet FAQ (Frequently Asked Questions) on the Microsoft AVI (Audio Video Interleave) file format. He has worked as a contractor at NASA Ames Research Center involved in the research and development of image and video processing algorithms and technology. He has published articles on the origin and evolution of life, the exploration of Mars (anticipating the discovery of methane on Mars), and cheap access to space. He has a Ph.D. in physics from the University of Illinois at Urbana-Champaign and a B.S. in physics from the California Institute of Technology (Caltech). He can be reached at [email protected].
Appendix: Octave Code for Figures
% % (C) 2014 by John F. McGowan, Ph.D. % % rough plot of improvements in video compression performance over time % % compare to: http://martinfowler.com/bliki/DesignStaminaHypothesis.html % % -- http://martinfowler.com/bliki/images/designStaminaGraph.gif % plateau's or near plateaus in video compression performance % period1 = 1995:2002; % THE MPEG ERA period2 = 2003:2007; % THE BREAKTHROUGH IN 2003 (H.264 etc.) period3 = 2008:2014; % ADVANCES IN REPRODUCING SKIN TONES 2008/2009 frame_rate = 30; % frames per second (NTSC is technically 29.97 frames/second) bits_per_byte = 8; color_channels_per_pixel = 3; % usually YCrCb (Y is black/white signal, Cr and Cb carry color) width = 720; height = 480; uncompressed_rate = width*height*color_channels_per_pixel*bits_per_byte*frame_rate; mpeg1_rate = 1000000; % one megabit per second h264_rate = 275000; % 275 kilobits per second (also Ogg Theora, Windows Media, Silverlight) % perceived quality is close to old analog NTSC television % under excellent broadcast conditions (lower than DVD or BluRay playback) % DVD is MPEG-2 with bit rate of 4-8 Megabits per second (same core technology as MPEG-1) % % compute compression ratio for periods cr1 = (uncompressed_rate / mpeg1_rate)*ones(size(period1)); cr2 = (uncompressed_rate / h264_rate)*ones(size(period2)); cr3 = (uncompressed_rate / h264_rate)*ones(size(period3)); % plot compression ratio over time % figure(1); plot(period1, cr1, "1", "linewidth", 3, period2, cr2, "2", "linewidth", 3, period3, cr3, "3", "linewidth", 3); title('VIDEO COMPRESSION PERFORMANCE'); xlabel('YEAR'); ylabel('COMPRESSION RATIO'); legend('MPEG-1 ERA', 'H.264 ERA', 'BETTER SKIN TONE', 'location', 'southeast'); % make plot for technology S-CURVE % figure(2); x = -1.0:0.02:1.0; y = 1.0 ./ (1.0 + exp(-1.0*10.0*x)); plot(x,y, "linewidth", 3); title('TECHNOLOGY S-CURVE'); xlabel('TIME'); ylabel('PERFORMANCE'); % THE END
% % make plot for maximum airspeed technology S-curve % % data from Wikipedia % http://en.wikipedia.org/wiki/Flight_airspeed_record % % data = dlmread('airspeed_cleaned.txt', '\t'); year = data(3:end, 1); % date/year mph = data(3:end, 3); % miles per hour of record kph = data(3:end, 4); % kilometers per hour of record plot(year, mph); xlabel('YEAR'); ylabel('MILES/HOUR'); title('FLIGHT AIRSPEED RECORD');
Date Pilot Airspeed Aircraft Location Notes mph km/h 1903 Wilbur Wright 6.82 10.98 Wright Flyer Kitty Hawk, North Carolina, USA 1905 Wilbur Wright 37.85 60.23 Wright Flyer III 1906 Alberto Santos-Dumont 25.65 41.292 Santos-Dumont 14-bis Bagatelle Castle, Paris, France First officially recognized airspeed record.   1907 Henry Farman 32.73 52.700 Voisin-Farman I Issy-les-Moulineaux, France   1909 Paul Tissandier 34.04 54.810 Wright Model A Pau, France   1909 Glenn Curtiss 43.367 69.821 Curtiss No. 2 Reims, France 1909 Gordon Bennett Cup.   1909 Louis Blériot 46.160 74.318 Blériot XI Reims, France   1909 Louis Blériot 47.823 76.995 Blériot XI Reims, France   1910 Hubert Latham 48.186 77.579 Antoinette VII Nice, France   1910 Léon Morane 66.154 106.508 Blériot Reims, France   1910 Alfred Leblanc 68.171 109.756 Blériot XI New York, New York, USA   1911 Alfred Leblanc 69.442 111.801 Blériot Blériot Pau, France   1911 Édouard Nieuport 73.385 119.760 Nieuport IIN Châlons, France   1911 Alfred Leblanc 77.640 125.000 Blériot  1911 Édouard Nieuport 80.781 130.057 Nieuport IIN Châlons, France   1911 Édouard Nieuport 82.693 133.136 Nieuport IIN Châlons, France   1912 Jules Védrines 87.68 145.161 Deperdussin Monocoque (1912) Pau, France   1912 Jules Védrines 100.18 161.290 Deperdussin monoplane Pau, France   1912 Jules Védrines 100.90 162.454 Deperdussin Monocoque Pau, France   1912 Jules Védrines 103.62 166.821 Deperdussin Monocoque Pau, France   1912 Jules Védrines 104.29 167.910 Deperdussin Monocoque Pau, France   1912 Jules Védrines 106.07 170.777 Deperdussin Monocoque Reims, France   1912 Jules Védrines 108.14 174.100 Deperdussin Monocoque (1912) Chicago, Illinois, USA   1913 Maurice Prévost 111.69 179.820 Deperdussin Monocoque (1913) Reims, France   1913 Maurice Prévost 119.19 191.897 Deperdussin Monocoque (1913) Reims, France   1913 Maurice Prévost 126.61 203.850 Deperdussin Monocoque (1913) Reims, France   1914 Norman Spratt 134.5 216.5 Royal Aircraft Factory S.E.4 Unofficial 1918 Roland Rohlfs 163 262.3 Curtiss Wasp Not officially recognised. 1919 Joseph Sadi-Lecointe 191.1 307.5 Nieuport-Delage NiD 29V Not officially recognised. 1920 Joseph Sadi-Lecointe 171.0 275.264 Nieuport-Delage NiD 29V Villacoublay, France.  First official record post World War 1.   1920 Jean Casale 176.1 283.464 Spad-Herbemont 20 bis Villacoublay, France    1920 Bernard de Romanet 181.8 292.682 Spad-Herbemont 20 bis Buc, France    1920 Joseph Sadi-Lecointe 184.3 296.694 Nieuport-Delage NiD 29V Buc, France   1920 Joseph Sadi-Lecointe 187.9 302.529 Nieuport-Delage NiD 29V Villacoublay, France   1920 Bernard de Romanet 191.9 309.012 SPAD S.XX Buc, France  1920 Joseph Sadi-Lecointe 194.4 313.043 Nieuport-Delage NiD 29V Villacoublay, France   1921 Joseph Sadi-Lecointe 205.2 330.275 Nieuport-Delage Sesquiplane Ville Sauvage, France   1922 Billy Mitchell 222.88 358.836 Curtiss R Detroit, Michigan, USA   1922 Billy Mitchell 224.28 360.93 Curtiss R-6 Selfridge Field, Detroit, Michigan, USA    1923 Joseph Sadi-Lecointe 232.91 375.00 Nieuport-Delage Istres  1923 1st Lt. Russell L. Maughan 236.587 380.74 Curtiss R-6 Wright Field, Dayton, Ohio, USA    1923 Lt. Harold J. Brow 259.16 417.07 Curtiss R2C-1 Mineola, New York, USA   1923 Lt. Alford J. Williams 266.59 429.02 Curtiss R2C-1 Mineola, New York, USA   1924 Florentin Bonnet 278.37 448.171 Bernard-Ferbois V.2  1927 Mario de Bernardi 297.70 479.290 Macchi M.52 seaplane Venice Database ID 11828  1928 Mario de Bernardi 318.620 512.776 Macchi M.52bis seaplane Venice Database ID 11827  1929 Giuseppe Motta 362.0 582.6 Macchi M.67 seaplane Unofficial 1929 George H. Stainforth 336.3 541.4 Gloster VI seaplane Calshot Database ID 11829 1929 Augustus Orlebar 357.7 575.5 Supermarine S.6 seaplane Calshot Database ID 11830  1931 George H. Stainforth 407.5 655.8 Supermarine S.6B seaplane Lee-on-the-Solent Database ID 11831  1933 Francesco Agello 423.6 682.078 Macchi M.C.72 seaplane Desenzano del Garda Database ID 11836  1934 Francesco Agello 440.5 709.209 Macchi M.C.72 seaplane Desenzano del Garda Database ID 4497  1935 Howard Hughes 352 566 Hughes H-1 Racer landplane Not an Official FAI record 1939 Fritz Wendel 469.220 755.138 Me 209 V1 Augsburg Piston-engined record until 1969 1941 Heini Dittmar 623.65 1003.67 Messerschmitt Me 163A V4 Peenemünde Rocket powered – Not an Official FAI record but over the 3 km FAI distance  1944 Heinz Herlitzius 624 1004 Messerschmitt Me 262 S2 Leipheim Not an Official FAI record  1944 Heini Dittmar 702 1130 Messerschmitt Me 163B V18 Lagerlechfeld Rocket powered – Not an Official FAI record  1945 H. J. Wilson 606.4 975.9 Gloster Meteor F Mk 4 Herne Bay, UK EE455 Britannia, a Mk 3 converted on production line to a long-span Mk 4. 1946 Edward Mortlock Donaldson 615.78 990.79 Gloster Meteor F Mk 4 Littlehampton, UK EE530, a long-span Mk 4. 1947 Col. Albert Boyd 623.74 1003.60 Lockheed P-80R Shooting Star Muroc, California, US  1947 Cmdr. Turner Caldwell 640.663 1031.049 Douglas Skystreak Muroc, California, US  1947 Major Marion Eugene Carl USMC 650.796 1047.356 Douglas Skystreak Muroc, California, US  1947 Chuck Yeager 670.0 1078 Bell X-1 Muroc, California, US Rocket powered – Not an official FAI C-1 record 1948 Maj. Richard L. Johnson, USAF 670.84 1079.6 North American F-86A-3 Sabre Cleveland, US   1952 J. Slade Nash 698.505 1124.13 North American F-86D Sabre Salton Sea, US  1953 William Barnes 715.745 1151.88 North American F-86D Sabre Salton Sea, US  1953 Neville Duke 727.6 1171 Hawker Hunter Mk.3 Littlehampton, UK  1953 Mike Lithgow 735.7 1184 Supermarine Swift F4 Castel Idris, Tripoli, Libya  1953 James B. Verdin, US Navy 752.9 1211.5 Douglas F4D Skyray Salton Sea, US  1953 Frank K. Everest USAF 755.1 1215.3 North American F-100 Super Sabre Salton Sea, US 1955 Horace A. Hanes 822.1 1323 North American F-100C Super Sabre Palmdale, US 1956 Peter Twiss 1132 1822 Fairey Delta 2 Chichester, UK  1957 USAF 1207.6 1943.5 McDonnell F-101A Voodoo Edwards Air Force Base, US  1958 Cap. WW Irwin, USAF 1404 2259.5 Lockheed YF-104A Starfighter Edwards Air Force Base, US  1959 Col. Georgii Mosolov 1484 2388 Ye-66 (Mikoyan-Gurevich MiG-21) USSR  1959 Maj. Joseph Rogers, USAF 1525.9 2455.7 Convair F-106 Delta Dart Edwards Air Force Base, US 1961 Robert G. Robinson, US Navy 1606.3 2585.1 McDonnell-Douglas F4H-1F Phantom II Edwards Air Force Base, US   1962 Lt. Col. Georgii Mosolov 1665.9 2681 Mikoyan Gurevich Ye-166 – name adopted for the record attempt, originally a version of a Ye-152 USSR   a.k.a. E-166. 1965 Robert L. Stephens and Daniel Andre 2070.1 3331.5 Lockheed YF-12A Edwards AFB, US  1976 Capt. Eldon W. Joersz and Maj. George T. Morgan 2193.2 3529.6 Lockheed SR-71 Blackbird #61-7958 Beale AFB, US