Bertrand Meyer's technology+ blog

(Reposted from the CACM blog [*].)

Software engineering was never a popular subject. It started out as “programming methodology”, evoking the image of bearded middle-aged men telling you with a Dutch, Swiss-German or Oxford accent to repent and mend your ways. Consumed (to paraphrase Mark Twain) by the haunting fear that someone, somewhere, might actually enjoy coding.

That was long ago. With a few exceptions including one mentioned below, to the extent that anyone still studies programming methodology, it’s in the agile world, where the decisive argument is often “I always say…”. (Example from a consultant’s page:  “I always tell teams: `I’d like a [user] story to be small, to fit in one iteration but that isn’t always the way.’“) Dijkstra did appeal to gut feeling but he backed it through strong conceptual arguments.

The field of software engineering, of which programming methodology is today just a small part, has enormously expanded in both depth and width. Conferences such as ICSE and ESEC still attract a good crowd, the journals are buzzing, the researchers are as enthusiastic as ever about their work, but… am I the only one to sense frustration? It is not clear that anyone outside of the community is interested. The world seems to view software engineering as something that everyone in IT knows because we all develop software or manage people who develop software. In the 2017 survey of CS faculty hiring in the U.S., software engineering accounted, in top-100 Ph.D.-granting universities, for 3% of hires! (In schools that stop at the master’s level, the figure is 6%; not insignificant, but not impressive either given that these institutions largely train future software engineers.) From an academic career perspective, the place to go is obviously  “Artificial Intelligence, Data Mining, and Machine Learning”, which in those top-100 universities got 23% of hires.

Nothing against our AI colleagues; I always felt “AI winter” was an over-reaction [1], and they are entitled to their spring. Does it mean software engineering now has to go into a winter of its own? That is crazy. Software engineering is more important than ever. The recent Atlantic  “software apocalypse” article (stronger on problems than solutions) is just the latest alarm-sounding survey. Or, for just one recent example, see the satellite loss in Russia [2] (juicy quote, which you can use the next time you teach a class about the challenges of software testing: this revealed a hidden problem in the algorithm, which was not uncovered in decades of successful launches of the Soyuz-Frigate bundle).

Such cases, by the way, illustrate what I would call the software professor’s dilemma, much more interesting in my opinion than the bizarre ethical brain-teasers (you see what I mean, trolley levers and the like) on which people in philosophy departments spend their days: is it ethical for a professor of software engineering, every morning upon waking up, to go to cnn.com in the hope that a major software-induced disaster has occurred,  finally legitimizing the profession? The answer is simple: no, that is not ethical. Still, if you have witnessed the actual state of ordinary software development, it is scary to think about (although not to wish for) all the catastrophes-in-waiting that you suspect are lying out there just waiting for the right circumstances .

So yes, software engineering is more relevant than ever, and so is programming methodology. (Personal disclosure: I think of myself as the very model of a modern methodologist [3], without a beard or a Dutch accent, but trying to carry, on today’s IT scene, the torch of the seminal work of the 1970s and 80s.)

What counts, though, is not what the world needs; it is what the world believes it needs. The world does not seem to think it needs much software engineering. Even when software causes a catastrophe, we see headlines for a day or two, and then nothing. Radio silence. I have argued to the point of nausea, including at least four times in this blog (five now), for a simple rule that would require a public auditing of any such event; to quote myself: airline transportation did not become safer by accident but by accidents. Such admonitions fall on deaf ears. As another sign of waning interest, many people including me learned much of what they understand of software engineering through the ACM Risks Forum, long a unique source of technical information on software troubles. The Forum still thrives, and still occasionally reports about software engineering issues, but most of the traffic is about privacy and security (with a particular fondness for libertarian rants against any reasonable privacy rule that the EU passes). Important topics indeed, but where do we go for in-depth information about what goes wrong with software?

Yet another case in point is the evolution of programming languages. Language creation is abuzz again with all kinds of fancy new entrants. I can think of one example (TypeScript) in which the driving force is a software engineering goal: making Web programs safer, more scalable and more manageable by bringing some discipline into the JavaScript world. But that is the exception. The arguments for many of the new languages tend to be how clever they are and what expressive new constructs they introduce. Great. We need new ideas. They would be even more convincing if they addressed the old, boring problems of software engineering: correctness, robustness, extendibility, reusability.

None of this makes software engineering less important, or diminishes in the least the passion of those of us who have devoted our careers to the field. But it is time to don our coats and hats: winter is upon us.

Notes

[1] AI was my first love, thanks to Jean-Claude Simon at Polytechnique/Paris VI and John McCarthy at Stanford.

[2] Thanks to Nikolay Shilov for alerting me to this information. The text is in Russian but running it through a Web translation engine (maybe this link will work) will give the essentials.

[3] This time borrowing a phrase from James Noble.

[*] I am reposting these CACM blog articles rather than just putting a link, even though as a software engineer I do not like copy-paste. This is my practice so far, and it might change since it raises obvious criticism, but here are the reasons: (A) The audiences for the two blogs are, as experience shows, largely disjoint. (B) I like this site to contain a record of all my blog articles, regardless of what happens to other sites. (C) I can use my preferred style conventions.

The full lineup of speakers at the 2018 LASER summer school on Software for Blockchains, Bitcoin and Distributed Trust is now ready, with the announcement of a new speaker, Primavera De Filippi from CNRS and Harvard on social and legal aspects.

The other speakers are Christian Cachin (IBM), Maurice Herlihy (Brown), Christoph Jentzsch (slock.it), me, Emil Gun Sirer (Cornell) and Roger Wattenhofer (ETH).

The school is the 14th in the LASER series and takes place June 2-10, 2018, on the island of Elba in Italy.

Early-fee registration deadline is February 10. The school’s page is here.

One of the most significant recent developments in software engineering is the concept of Devops*. Dismissing the idea as “just the latest buzzword” would be wrong. It may be a buzzword but it reflects a fundamental change in the way we structure system development; with web applications in particular the traditional distinctions between steps of development, V&V** and deployment fade out. If you are using Microsoft Word, you know or can easily find out the version number; but which version of your search engine are you using?

With the new flexibility indeed come new risks, as when a bug in the latest “devopsed”  version of Google Docs caused me to lose a whole set of complex diagrams irretrievably; an earlier article on this blog (“The Cloud and Its Risks“, October 2010) told the story.

In the new world of continuous integrated development/V&V/deployment, software engineering principles are more necessary than ever, but their application has to undergo a profound adaptation.

With Jean-Michel Bruel (Toulouse), Elisabetta Di Nitto (Milan) and Manuel Mazzara (Innopolis), we are organizing a workshop on the topic, DEVOPS 18, on 5-6 March 2018 near Toulouse. The Call for Papers is available here, with Springer LNCS proceedings. The submission deadline is January 15, but for that date a 2-page extended abstract is sufficient. I hope that the event will help the community get a better grasp of the software engineering techniques and practices applicable to this new world of software development.

Notes

*I know, it’s supposed to be DevOps (I am not a great fan of upper case in the middle of words).
** Validation & Verification.

Many programs take “execution arguments” which the program users provide at the start of execution. In EiffelStudio you can enter them under Execution -> Execution parameters.

The program can access them through the Kernel Library class ARGUMENTS. Typically, the root class of the system inherits from ARGUMENTS and its creation procedure will include something like

if argument_count /= N then
……..print (“XX expects exactly N arguments: AA, BB, …%N”)
else
……..u := argument (1) ; v := argument (2) ; …
……..“Proceed with normal execution, using u, v, …”
end

where N is the number of expected arguments, XX is the name of the program, and AA, …. are the roles of arguments. u, v, … are local variables. The criterion for acceptance could be “at least N” instead of exactly N. The features argument_count and arguments come from class ARGUMENTS.

In all but trivial cases this scheme (which was OK years ago, in a less sophisticated state of the language) does not work! The reason is that the error branch will fail to initialize attributes. Typically, the “Proceed with…” part in the other branch is of the form

               attr1 := u
                attr2 := v
                …
                create obj1.make (attr1, …)
                create obj2.make (attr2, …)
                “Work with obj1, obj2, …”

If you try to compile code of this kind, you will get a compilation error:

Eiffel is void-safe: it guarantees that no execution will ever produce null-pointer dereference (void call). To achieve this guarantee, the compiler must make sure that all attributes are “properly set” to an object reference (non-void) at the end of the creation procedure. But the error branch fails to initialize obj1 etc.

You might think of replacing the explicit test by a precondition to the creation procedure:

               require
                                argument_count = N

but that does not work; the language definition explicit prohibits preconditions in a root creation procedure. The Ecma-ISO standard (the official definition of the language, available here) explains the reason for the corresponding validity rule (VSRP, page 32):

A routine can impose preconditions on its callers if these callers are other routines; but it makes no sense to impose a precondition on the external agent (person, hardware device, other program…) that triggers an entire system execution, since there is no way to ascertain that such an agent, beyond the system’s control, will observe the precondition.

The solution is to separate the processing of arguments from the rest of the program’s work. Add a class CORE which represents the real core of the application and separate it from the root class, say APPLICATION. In APPLICATION, all the creation procedure does is to check the arguments and, if they are fine, pass them on to an instance of the core class:

                note
                                description: “Root class, processes execution arguments and starts execution”
                class APPLICATION create make feature
                                core: CORE
                                                — Application’s core object
                                make
……..……..……..……..……..……..— Check arguments and proceed if they make sense.
                                                do
                                                             if argument_count /= N then
                                                                                print (“XX expects exactly N arguments: AA, BB, …%N”)
                                                                else
                                                                                create core.make (argument (1), argument (2) ; …)
                                                                                                — By construction the arguments are defined!
                                                                                core.live
                                                                                                — Perform actual work
                                                                                               — (`live’ can instead be integrated with `make’ in CORE.)

                                                                end
                                                end
                 end
 
We may call this little design pattern “Split the Root”. Nothing earth-shattering; it is simply a matter of separating concerns (cutting off the Model from the View). It assumes a system that includes text-based output, whereas many applications are graphical. It is still worth documenting, for two reasons.

First, in its own modest way, the pattern is useful for simple programs; beginners, in particular, may not immediately understand why the seemingly natural way of processing and checking arguments gets rejected by the compiler.

The second reason is that Split the Root illustrates the rules that preside over a carefully designed language meant for carefully designed software. At first it may be surprising and even irritating to see code rejected because, in a first attempt, the system’s root procedure has a precondition, and in a second attempt because some attributes are not initialized — in the branch where they do not need to be initialized. But there is a reason for these rules, and once you understand them you end up writing more solid software.

Just about a year ago I posted this announcement about my just released Agile course:

In spite of all the interest in both agile methods and MOOCs (Massive Open Online Courses) there are few courses on agile methods; I know only of some specialized MOOCs focused on a particular language or method.

I produced for EdX, with the help of Marco Piccioni, a new MOOC entitled Agile Software Development. It starts airing today and is supported by exercises and quizzes. The course uses some of the material from my Agile book.

The course is running again! You can find it on EdX here.

Such online courses truly “run”: they are not just canned videos but include exercises and working material on which you can get feedback.

Like the book (“Agile: The Good, the Hype and the Ugly“, Springer), the course is a tutorial on agile methods, presenting an unbiased analysis of their benefits and limits.

As part of the continuation of the ERC Advanced Investigator Grant project “Concurrency Made Easy” (started at ETH Zurich, see the project pages at cme.ethz.ch), I have positions at Politecnico di Milano for:

• Postdocs (having a doctoral degree)
• Research associates (officially: “Assegno di Ricerca”, with the requirement of having a master degree), which can lead to a PhD position.

The deadline for applications is October 11. Please contact me directly if interested. What I expect:

• The requisite degrees as stated above.
• Innovative and enterprising spirit, passion for quality work in software engineering.
• Either or both of excellent programming abilities and strong CS theoretical background.
• Knowledge of as many of possible of: object-oriented programming, concurrency/parallelism, software verification/formal methods, Eiffel.
• Familiarity with the basics of the project as described in the project pages at the URL above.

Much of the progress in robotics is due to software advances, and software issues remain at the heart of the formidable challenges that remain. The 2017 LASER summer school, held in September in Elba, brings together some of the most prestigious international experts in the area.

The LASER school has established itself as one of the principal forums to discussed advanced software issues. The 2017 school takes place from 9 to 17 September in the idyllic setting of the Hotel del Golfo in Procchio, Elba Island, Italy.

Robotics is progressing at an amazing pace, bringing improvements to almost areas of human activity. Today’s robotics systems rely ever more fundamentally on complex software, raising difficult issues. The LASER 2017 summer school covers both the current state of robotics software technology and open problems. The lecturers are top international experts with both theoretical contributions and major practical achievements in developing robotics systems.
The LASER school is intended for professionals from the industry (engineers and managers) as well as university researchers, including PhD students. Participants learn about the most important software technology advances from the pioneers in the field. The school’s focus is applied, although theory is welcome to establish solid foundations. The format of the school favors extensive interaction between participants and speakers.

We have lined up an impressive roster of speakers from the leading edge of both industry and academia:

• Rodolphe Gélin, Aldebaran Robotics
• Ashish Kapoor, Microsoft Research
• Davide Brugali, University of Bergamo, on Managing software variability in robotic control systems
• Nenad Medvidovic, University of Southern California, on Software Architectures of Robotics Systems
• Bertrand Meyer, Politecnico di Milano & Innopolis University, on Concurrent Object-Oriented Robotics Software
• Issa Nesnas, NASA Jet Propulsion Laboratory, on Experiences from robotic software development for research and planetary flight robots
• Hiroshi (“Gitchang”) Okuno, Waseda University & Kyoto University, on Open-Sourced Robot Audition Software HARK: Capabilities and Applications

The school takes place at the magnificent Hotel del Golfo in the Gulf of Procchio, Elba. Along with an intensive scientific program, participants will have time to enjoy the countless natural and cultural riches of this wonderful, history-laden jewel of the Mediterranean.

For more information about the school, the speakers and registration see the LASER site.

Microsoft Office tools offer  features for (1) spelling correction and (2) multi-language support. They are not very good at working together, another example of the perils of feature interaction.

Spelling correction will by default

when misspelled, but in the case of common misspellings known to the tools it will simply correct words without bothering the user. For example if you type “bagage” it will change it silently to “baggage”. This feature can be turned off, and the list of known misspellings can be edited, but most people use the defaults, as I am assuming here.

Multi-language support enables you to “install” several languages. Then when you type a text it will after a few words guess the relevant language. From then on it can  apply the proper spell checks and corrections.

These features are both useful, and by and large they both work. (The second one is not always reliable. I regularly end up, particularly in Microsoft Word, with entire paragraphs underlined in red because for some inscrutable reason the tool assigns them the wrong language. In such cases you must tell it manually what language it should apply.)

Their combination can lead to funny results. Assume your default language is English but you also have French installed, and you are typing an email in French under Outlook. Your email will say “Le bagage est encore dans l’avion”, meaning “The baggage is still in the plane”. The word “baggage” has one more “g” in English than in French. You start typing  “Le bagage”, but because at that point the tool assumes English it corrects it silently:

Next you type “est encore”:

The  word “est” (is) gets flagged because (unlike “encore”, here meaning “still”) it does not exist in English. When you add the next word, “dans” (in), the tool is still assuming an English text, so it flags it too:

Now you type “l” and when you add the apostrophe, you can almost hear a “silly me, I see now, that’s French!”. Outlook  switches languages and unflags the previously flagged words, removing the red squiggle under the ones that are correct in French:

But that is too late for “baggage”: the automatic respelling of “bagage”, coming from the default assumption that the text was in English, no longer makes sense now that we know it is in French. So the word gets flagged as a misspelling. You have to go back and correct it yourself. That is frustrating, since you typed the correct spelling in the first place (“bagage”), and it is the tool that messed it up.

This bug hits me often. It is indeed a bug, which can introduce misspellings into a text when the user typed it correctly. When the tool recognizes that the text is in another language than the one assumed so far, and performs a second pass over the part already analyzed, it should reconsider both the words previously flagged as misspellings but also those previously corrected. There is no justification for doing one and not the other.

Among the world’s most momentous problems, this one does not rank very high. It is only a small annoyance, and only a tiny set of people will ever notice it. But it provides another illustration of how tricky it is to go from good individual features to a good overall design.

Related:

• Ado About the Resource That Was (Not)
• Infinite Loop in Microsoft Word
• The Perils of Feature Interaction

One of the most delicate aspects of design is feature interaction. As users, we suffer daily from systems offering features that individually make sense but clash with each other. In my agile book [1] I explained in detail, building on the work of Pamela Zave, why this very problem makes one of the key ideas of agile methods,  the reliance on “user stories” for requirements, worthless and damaging.

A small recent incident reminded me of the perils of feature interaction. I used my Lenovo W540 laptop without power for a short while, then reached a sedentary location and plugged it in. Hence my surprise when, some hours later, it started beeping to alert me that it was running out of battery. The natural reactions — check the outlet and the power cord — had no effect. I found the solution, but just in time: otherwise, including if I had not heard the warning sound, I would have been unable to use the laptop any further. That’s right: I would not have been able to restart the computer at all, even with access to a power outlet, and even though it was perfectly functional and so was its (depleted) battery. The reason is that the problem arose from a software setting, which (catch-22 situation) I could not correct without starting the computer [2].

The only solution would have been to find another, non-depleted battery. That is not a trivial matter if you have traveled with your laptop outside of a metropolis: the W540 has a special battery which ordinary computer shops do not carry [3].

The analysis of what made such a situation possible must start with the list of relevant hardware and software product features.

Hardware:

• HA. This Lenovo W series includes high-end laptops with high power requirements, which the typical 65-watt airplane power jack does not satisfy.
• HB. With models prior to the W540, if you tried to connect a running laptop to the power supply in an airplane, it would not charge, and the power indicator would start flickering.  But you could still charge it if you switched it off.
• HC. The W540 effectively requires 135 watts and will not take power from a 65-watt power source under any circumstances.

Software:

• SA. The operating system (this discussion assumes Windows) directly reflects HC by physically disabling charging if the laptop is in the “Airplane” power mode.
• SB. If you disable wireless, the operating system automatically goes into the “Airplane” power mode.
• SC. In the “Airplane” power mode, the laptop, whether or not connected through a charger to a power outlet of any wattage, will not charge. The charging function is just disabled.
• SD. One can edit power modes to change parameters, such as time to automatic shutoff, but the no-charging property in Airplane mode is not editable and not even mentioned in the corresponding UI dialog. It seems to be a behind-the-scenes property magically attached to the power-mode name “Airplane”.
• SE. There is a function key for disabling wireless: F8. As a consequence of SB it also has the effect of switching to “Airplane” mode.
• SF. Next to F8 on the keyboard is F7.
• SG. F7 serves to display the screen content on another monitor (Windows calls it a “projector”). F7 offers a cyclic set of choices: laptop only, laptop plus monitor etc.
• SH. In the old days (like five years ago), such function keys setting important operating system parameters on laptops used to be activated only if you held them together with a special key labeled “Fn”. For some reason (maybe the requirement was considered too complicated for ordinary computer users) the default mode on Lenovo laptops does not use the “Fn” key anymore: you just press the desired key, such as F7 or F8.
• SI. You can revert to the old mode, requiring pressing “Fn”, by going into the BIOS and performing some not-absolutely-trivial steps, making this possibility the preserve of techies. (Helpfully, this earlier style is called “Legacy mode”, as a way to remind you that your are an old-timer, probably barely graduated from MS-DOS and still using obsolete conventions. In reality, the legacy mode is the right one to use, whether for techies or novices: it is all too easy to hit a function key by mistake and get totally unexpected results. The novice, not the techie, is the one who will be completely confused and panicked as a result. The first thing I do with a new laptop is to go to the BIOS and set legacy mode.)

By now you have guessed what happened in my case, especially once you know that I had connected the laptop to a large monitor and had some trouble getting that display to work. In the process I hit Fn-F7 (feature SG) several times.  I must have mistakenly (SF) pressed F8 instead of F7 at some point. Normally, Legacy mode (SI) should have made me immune to the effects of hitting a function key by mistake, but I did use the neighboring key F7 for another purpose. Hitting F8 disabled wireless (SE) and switched on Airplane power mode (SB). At that point the laptop, while plugged in correctly, stopped charging (SC, SD).

How did I find out? Since I was looking for a hardware problem I could have missed the real cause entirely and ended up with a seemingly dead laptop. Fortunately I opened the Power Options dialog to see what it said about the battery. I noticed that among the two listed power plans the active one was not “Power Saver”, to which I am used, but “Airplane”. I did not immediately pay  attention to that setting; since I had not used the laptop for a while I just thought that maybe the last time around I had switched on “Airplane”, even though that made little sense since I was not even aware of the existence of that option. After trying everything else, though, I came back to that intriguing setting, changed to the more usual “Power Saver”, and the computer started to charge again. I was lucky to have a few percent of battery still left at that point.

Afterwards I found a relevant discussion thread on a Lenovo user forum.

As is often the case in such feature-interaction mishaps, most of the features make sense individually [4]. What causes trouble is some unforeseen combination of features.

There is no sure way to avoid such trouble, but there is a sure way to cause it: design a system feature by feature, as with user stories in agile development. The system must do this and it must do that. Oh, by the way, it must also do that. And that. User stories have one advantage: everyone understands them. But that is also their limitation. Good requirements and design require professionals who can see the whole beyond the parts.

A pernicious side of this situation is that many people believe that use cases and user stories are part of object-oriented analysis, whereas the OO approach to requirements and design is the reverse: rise above individual examples to uncover the fundamental abstractions.

As to my laptop, it is doing well, thanks. And I will be careful with function keys.

Reference and notes

[1] Bertrand Meyer: Agile! The Good, the Hype and the Ugly, Springer, 2014,  Amazon page: here, book page: here. A description of the book appeared here on this blog at the time of publication.

[2] Caveat: I have not actually witnessed this state in which a plugged-in laptop will not restart. The reason is simply that I do not have an alternate battery at the moment so I cannot perform the experiment with the almost certain result of losing the use of my laptop. I will confirm the behavior as soon as I have access to a spare battery.

[3] It has been my systematic experience over the past decade and a half that Lenovo seems to make a point, every couple of years, to introduce new models with incompatible batteries and docking stations. (They are also ever more incredibly bulky, with the one for the W540 almost as heavy as the laptop itself. On the other hand the laptops are good, otherwise I would not be bothering with them.)

[4] One exception here is feature SB: switching wireless off does not necessaril y mean you want to select a specific power mode! It is a manifestation of the common syndrome  of software tools that think they are smarter than you, and are not. Another exception is SE: to let a simple key press change fundamental system behavior is to court disaster. But I had protected myself by using legacy mode and was hit anyway.

Когда-то очень давно великий советский ученый Андрей Петрович Ершов мне рассказал следующий анекдот. Действие происходит в московском метро. Стоит бабушка, а за ней высокий студент из Университета Имени Патрицы Лумумбы. Он стучит ей по плечу, она поворачивает голову, видит его, вскрикивает (она никогда в жизни не видела Африканца), и падает в обморок.

Другие пассажиры успокаивают ее («ничего страшного, он такой же человек, как и мы!») и она постепенно приходит в себя. Африканский студент объясняет: «Прошу прощения, я только хотел Вас спросить: Вы на следующей выходите?».

Она испуганно смотрит на него и опять падает в обморок, крича: « Ах! Говорит!».

Ершовский анекдот точно описывает ежедневный опыт иностранца в России, который сносно владеет русским языком; но все всегда и везде тотчас же узнают, что он иностранец. Никто и не полагает, что такое существо способно произвести толковые звуки. А если он, вопреки всем ожиданиям, открывает рот и что-нибудь говорит в своей имитации русского языка, выражение на лице собеседника сразу же меняется в испугу : «Ах! Говорит!».

(First published on the CACM blog.)

A book by Laurent Bossavit [1] lists what he calls “leprechauns” of software engineering: pearls of conventional wisdom that do not necessarily survive objective analysis. Whether or not we agree with him on every specific example, his insights are fruitful and the general approach commendable: it is healthy to question revered truths.

A revered truth not cited in his book but worth questioning is “Brooks’ Law” from The Mythical Man-Month [2]. Disclosure: I never cared much for that book, even when I read it at the time of its first publication. I know it is supposed to be a font of wisdom, but with one exception (the “second-system effect”, which actually contradicts some of the book’s other precepts) I find its advice either trivial or wrong. For those readers still with me after this admission of sacrilege, one of the most quoted pronouncements is the modestly titled “Brooks’ Law” according to which adding manpower to a late project makes it later.

Like many unwarranted generalizations, this supposed law can hold in special cases, particular at the extremes: you cannot do with thirty programmers in one day what one programmer would do in a month. That’s why, like many urban legends, it may sound right at first. But an extreme example is not a general argument. Applied in meaningful contexts, the law is only valid as a description of bad project management. If you just add people without adapting the organization accordingly, you will run into disaster. True, but not a momentous discovery.

The meaningful observation is that when a team’s size grows, communication and collaboration issues grow too, and the manager must put in place the appropriate mechanisms for communication and collaboration. Also not a strikingly original idea. Good managers know how to set up these mechanisms. Such an ability is almost the definition of  “good manager”: the good manager is the one to whom Brooks’ Law does not apply. Anyone with experience in the software industry has seen, along with disasters, cases in which a good manager was able to turn around a failing project by, among other techniques, adding people. The tools and methods of modern software engineering and modern project management are of great help in such an effort. Pithy, simplistic, superficial generalizations are not.

I thought of the matter recently when chancing upon Nathan Fielder’s Maid Service video [3]. (Warning: Fielder is sometimes funny — and sometimes not — but always obnoxious.) While programming is not quite the same as house cleaning, there is still a lesson there. With good organization, a competent manager can indeed reduce time, perhaps not linearly but close, by multiplying the number of workers.

One leprechaun dispatched, many to go.

References

[1] Laurent Bossavit:  The Leprechauns of Software Engineering – How folklore turns into fact and what to do about it, e-book available here (for a fee, with a free preview).

[2] Fred Brooks: The Mythical Man-Month – Essays on Software Engineering, Addison-Wesley, 1975, new editions 1982 and 1995.

[3] Nathan for You: Maid Service, video available here.

The LASER summer school, now in its 13th edition, will take place this September (postponed from last year). The theme is new for the school, and timely: software for robotics. Below is the announcement.

The school site is here.

Full announcement:

The 2017 LASER summer school will be devoted to Software for Robotics. It takes place from 9 to 17 September in the exceptional setting of the Hotel del Golfo in Procchio, Elba Island, Italy.

Robotics is progressing at an amazing pace, bringing improvements to almost areas of human activity. Today’s robotics systems rely ever more fundamentally on complex software, raising difficult issues. The LASER 2017 summer school both covers the current state of robotics software technology and open problems. The lecturers are top international experts with both theoretical contributions and major practical achievements in developing robotics systems.
The LASER school is intended for professionals from the industry (engineers and managers) as well as university researchers, including PhD students. Participants learn about the most important software technology advances from the pioneers in the field. The school’s focus is applied, although theory is welcome to establish solid foundations. The format of the school favors extensive interaction between participants and speakers.

We have lined up an impressive roster of speakers from the leading edge of both industry and academia:

• Rodolphe Gélin, Aldebaran Robotics
• Ashish Kapoor, Microsoft Research
• Davide Brugali, University of Bergamo, on Managing software variability in robotic control systems
• Nenad Medvidovic, University of Southern California, on Software Architectures of Robotics Systems
• Bertrand Meyer, Politecnico di Milano & Innopolis University, on Concurrent Object-Oriented Robotics Software
• Issa Nesnas, NASA Jet Propulsion Laboratory, on Experiences from robotic software development for research and planetary flight robots

The school takes place at the magnificent Hotel del Golfo in the Gulf of Procchio, Elba. Along with an intensive scientific program, participants will have time to enjoy the countless natural and cultural riches of this wonderful, history-laden jewel of the Mediterranean.

For more information about the school, the speakers and registration see the LASER site.

The Orbitz page for booking a flight itinerary has an interesting menu option:

Longest duration? If you find that the direct route is too short, you can always add a stop in Vladivostok. Under a few basic assumptions it has to be a theorem that, given any itinerary from A to B, there exists a longer itinerary from A to B.

Experiments with the site suggest, however, that the result of selecting that option is (regrettably from a theoretical perspective, but perhaps preferably for travelers) finite.

The AutoProof technology pursues the goal of “Verification As a Matter Of Course”, integrated into the EVE development environment. (The AutoProof  project page here; see particularly the online interactive tutorial.) A one-day workshop devoted to the existing AutoProof and current development will take place on October 1 near Toulouse in France. It is an informal event (no proceedings planned at this point, although based on the submissions we might decide to produce a volume), on a small scale, designed to bring together people interested in making the idea of practical verification a reality.

The keynote will be given by Rustan Leino from Microsoft Research, the principal author of the Boogie framework on which the current implementation of AutoProof relies.

For submissions (or to attend without submitting) see the workshop page here. You are also welcome to contact me for more information.

In spite of all the interest in both agile methods and MOOCs (Massive Open Online Courses) there are few courses on agile methods; I know only of some specialized MOOCs focused on a particular language or method.

I produced for EdX, with the help of Marco Piccioni, a new MOOC entitled Agile Software Development. It starts airing today and is supported by exercises and quizzes. The course uses some of the material from my Agile book.

Registration is free and open to anyone at this address.

Many robotics applications are by nature concurrent; in his ongoing PhD work, Andrey Rusakov [1] is building a comprehensive concurrent robot programming framework, Roboscoop [2], based on the SCOOP model for simple concurrent object-oriented programming [3] and the Ros operating system. As part of this work it is important to know how much robotics applications use concurrency, stay away from concurrency — perhaps because programmers are afraid of the risks — and could benefit from more concurrency. Rusakov has prepared a questionnaire [4] to help find out. If you have experience in robot programming, please help him by answering the questionnaire, which takes only a few minutes.

References

[1] Rusakov’s home page here.

[2] Roboscoop project page, here,

[3] Simple Concurrent Object-Oriented Programming, see here.

[4] The questionnaire is here.

The 2016 session of the LASER summer school, now in its 13th edition, has just been announced. The theme is new for the school, and timely: software for robotics. Below is the announcement.

School site: here

The 2016 LASER summer school will be devoted to Software for Robotics. It takes place from 10 to 18 September in the magnificent setting of the Hotel del Golfo in Procchio, Elba Island, Italy.

Robotics is progressing at an amazing pace, bringing improvements to almost areas of human activity. Today’s robotics systems rely ever more fundamentally on complex software, raising difficult issues. The LASER 2016 summer school both covers the current state of robotics software technology and open problems. The lecturers are top international experts with both theoretical contributions and major practical achievements in developing robotics systems.
The LASER school is intended for professionals from the industry (engineers and managers) as well as university researchers, including PhD students. Participants learn about the most important software technology advances from the pioneers in the field. The school’s focus is applied, although theory is welcome to establish solid foundations. The format of the school favors extensive interaction between participants and speakers.
The speakers include:

• Joydeep Biswas, University of Massachussetts, on Development, debugging, and maintenance of deployed robots
• Davide Brugali, University of Bergamo, on Managing software variability in robotic control systems
• Nenad Medvidovic, University of Southern California, on Software Architectures of Robotics Systems
• Bertrand Meyer, Politecnico di Milano and Innopolis University, with Jiwon Shin, on Concurrent Object-Oriented Robotics Software: Concepts, Framework and Applications
• Issa Nesnas, NASA Jet Propulsion Laboratory, on Experiences from robotic software development for research and planetary flight robots
• Richard Vaughan, Simon Fraser University

Organized by Politecnico di Milano, the school takes place at the magnificent Hotel del Golfo (http://www.hoteldelgolfo.it/) in Golfo di Procchio, Elba. Along with an intensive scientific program, participants will have time to enjoy the natural and cultural riches of this history-laden jewel of the Mediterranean.

For more information about the school, the speakers and registration see here.

.

— Bertrand Meyer

(A version of this article also appeared on the CACM blog.)

Miracles happen!

Many months ago I accepted, perhaps too fast, a kind invitation to talk at the European Computer Science Summit, the annual conference of Informatics Europe, this week in Vienna. It came with a catch: I was not to choose my own topic but to talk on an imposed theme, ethics in relation to computer science.

As the summer advanced, I became increasingly worried about the talk. What was I going to say? For a nerd, an invited lecture on a free topic is easy: talk about how alias analysis makes automatic frame inference possible, explain the bizarre mixture of the best and worst in agile methods, present a simple method of concurrent programming, describe an environment enabling common mortals to prove programs correct, reflect on our 13-year experience of teaching programming and the supporting MOOCs, and so on. All straightforward stuff which one can present in one’s sleep. But ethics!

The summer receded, but the worry did not. What in the world would I talk about?

And then!

From the deepest of my heart: thank you, Volkswagen.

A third ACM webinar this year (after two on agile methods): I will be providing a general introduction to Design by Contract. The date is this coming Thursday, September 17, and the time is noon New York (18 Paris/Zurich, 17 London, 9 Los Angeles, see here for hours elsewhere). Please tune in! The event is free but requires registration here.

Programming, wrote Dijkstra many years ago, is a branch of applied mathematics. That is only half of the picture: the other half is engineering, and this dual nature of programming is part of its attraction.

Descriptions of the mathematical side are generally, in my view, too complicated. This article [1] presents a mathematical theory of programs and programming based on concepts taught in high school: elementary set theory. The concepts covered include:

• Programming.
• Specification.
• Refinement.
• Non-determinism.
• Feasibility.
• Correctness.
• Programming languages.
• Kinds of programs: imperative, functional, object-oriented.
• Concurrency (small-step and large-step)
• Control structures (compound, if-then-else and Dijkstra-style conditional, loop).
• State, store and environment.
• Invariants.
• Notational conventions for building specifications and programs incrementally.
• Loop invariants and variants.

One of the principal ideas is that a program is simply the description of a mathematical relation. The program text is a rendering of that relation. As a consequence, one may construct programming languages simply as notations to express certain kinds of mathematics. This approach is the reverse of the usual one, where the program text and its programming languages are the starting point and the center of attention: theoreticians develop techniques to relate them to mathematical concepts. It is more effective to start from the mathematics (“unparsing” rather than parsing).

All the results (74 properties expressed formally, a number of others in the text) are derived as theorems from rules of elementary set theory; there are no new axioms whatsoever.

The paper also has a short version [2], omitting proofs and many details.

References

[1] Theory of Programs, available here.
[2] Theory of Programs, short version of [1] (meant for quick understanding of the ideas, not for publication), available here.

After my earlier ACM Webinar on Agile Methods! The Good, the Hype and the Ugly there were so many questions from the audience, left unanswered for lack of time, that a follow-up session has been set up. It will take place tomorrow (Friday, 27 March 2015) at noon New York time (18 Paris/Berlin/Zurich, 5 PM London etc.). Like the first one it is free and you can find the registration information here.

ACM is offering this coming Wednesday a one-hour webinar entitled Agile Methods: The Good, the Hype and the Ugly. It will air on February 18 at 1 PM New York time (10 AM West Coast, 18 London, 19 Paris, see here for more cities). The event is free and the registration link is here.

The presentation is based on my recent book with an almost identical title [1]. It will be a general discussion of agile methods, analyzing both their impressive contributions to software engineering and their excesses, some of them truly damaging. It is often hard to separate the beneficial from the indifferent and the plain harmful, because most of the existing presentations are of the hagiographical kind, gushing in admiration of the sacred word. A bit of critical distance does not hurt.

As you can see from the Amazon page, the first readers (apart from a few dissenters, not a surprise for such a charged topic) have relished this unprejudiced, no-nonsense approach to the presentation of agile methods.

Another characteristic of the standard agile literature is that it exaggerates the contrast with classic software engineering. This slightly adolescent attitude is not helpful; in reality, many of the best agile ideas are the direct continuation of the best classic ideas, even when they correct or adapt them, a normal phenomenon in technology evolution. In the book I tried to re-place agile ideas in this long-term context, and the same spirit will also guide the webinar. Ideological debates are of little interest to software practitioners; what they need to know is what works and what does not.

References

[1] Bertrand Meyer, Agile! The Good, the Hype and the Ugly, Springer, 2014, see Amazon page here, publisher’s page here and my own book page here.

Actually not that new: this paper [1] was published in August of last year. It is part of Christian Estler’s work for this PhD thesis, defended a few weeks ago, and was pursued in collaboration with Martin Nordio and Carlo Furia. It received the best paper award at the International Conference on Global Software Engineering; in fact this was the third time in a row that this group received the ICGSE award, so it must have learned a few things about collaborative development.

The topic is an issue that affects almost all software teams: how to make sure that people are aware of each other’s changes to a shared software base, in particular to avoid the dreaded case of a merge conflict: you and I are working on the same piece of code, but we find out too late, and we have to undergo the painful process of reconciling our conflicting changes.

The paper builds once again on the experience of our long-running “Distributed and Outsourced Software Engineering” course project, where students from geographically spread universities collaborate on a software development [2]. It relies on data from 105 student developers making up twelve development teams located in different countries.

The usual reservations about using data from students apply, but the project is substantial and the conditions not entirely different from those of an industrial development.

The study measured the frequency and impact of merge conflicts, the effect of insufficient awareness (no one told me that you are working on the same module that I am currently modifying) and the consequences for the project: timeliness, developer morale, productivity.

Among the results: distribution does not matter that much (people are not necessarily better informed about their local co-workers’ developments than about remote collaborators); lack of awareness occurs more often than merge conflicts, and causes more damage.

References

[1] H-Christian Estler, Martin Nordio, Carlo A. Furia and Bertrand Meyer: Awareness and Merge Conflicts in Distributed Software Development, in proceedings of ICGSE 2014, 9th International Conference on Global Software Engineering, Shanghai, 18-21 August 2014, IEEE Computer Society Press (best paper award), see here.

[2] Distributed and Outsourced Software Engineering course and project, see here. (The text mentions “DOSE 2013” but the concepts remains applicable and it will be updated.)

To verify sequential programs, we have to prove that they do the right thing, but also that they do it within our lifetime — that they terminate. The termination problem is considerably harder with concurrent programs, since they add a new form of non-termination: deadlock. A set of concurrent processes or threads will deadlock if they end up each holding a resource that another wants and wanting a resource that another holds.

There is no general solution to the deadlock problem, even a good enough general solution. (“Good enough” is the best we can hope for, since like many important problems deadlock is undecidable.) It is already hard enough to provide run-time deadlock detection, to be able at least to cancel execution when deadlock happens. The research reported in this new paper [1] pursues the harder goal of static detection. It applies to an object-oriented context (specifically the SCOOP model of concurrent OO computation) and relies fundamentally on the alias calculus, a static alias analysis technique developed in previous publications.

The approach is at its inception and considerable work remains to be done. Still, the example handled by the paper is encouraging: analyzing two versions of the dining philosophers problem and proving — manually — that one can deadlock and the other cannot.

References

[1] Bertrand Meyer: An automatic technique for static deadlock prevention, in PSI 2014 (Ershov Informatics Conference), eds. Irina Virbitskaite and Andrei Voronkov, Lecture Notes in Computer Science, Springer, 2015, to appear.; draft available here.

I write a sentence, but Microsoft Word’s indefatigable grammar checker catches me:

.

I see! Word  underlined “well-argued” in blue because the hyphen is bad style. Thanks! I choose the obligingly provided correction (just click the first menu entry). “Well argued“. Then:

Sigh.

In support of his view of software methodology, Leslie Lamport likes to use the example of non-recursive Quicksort. Independently of the methodological arguments, his version of the algorithm should be better known. In fact, if I were teaching “data structures and algorithms” I would consider introducing it first.

As far as I know he has not written down his version in an article, but he has presented it in lectures; see [1]. His trick is to ask the audience to give a non-recursive version of Quicksort, and of course everyone starts trying to remove the recursion, for example by making the stack explicit or looking for invertible functions in calls. But his point is that recursion is not at all fundamental in Quicksort. The recursive version is a specific implementation of a more general idea.

Lamport’s version — let us call it Lampsort —is easy to express in Eiffel. We may assume the following context:

a: ARRAY [G -> COMPARABLE]        — The array to be sorted.
pivot: INTEGER                                      —  Set by partition.
picked: INTEGER_INTERVAL            — Used by the sorting algorithm, see below.
partition (i, j: INTEGER)
……..require      — i..j is a sub-interval of the array’s legal indexes:
……..……..i < j
……..……..i >= a.lower
……..……..j <= a.upper
……..do
……..……..… Usual implementation of partition …
……..ensure     — The expected effect of partition:
……..……..pivot >= i
……..……..pivot < j
……..……..— a [i..j] has been reshuffled so that elements in i..pivot are less than
……..……..— or equal to those in pivot+1 .. j.
……..end

We do not write the implementation of partition since the point of the present discussion is the overall algorithm. In the usual understanding, that algorithm consists of doing nothing if the array has no more than one element, otherwise performing a partition and then recursively calling itself on the two resulting intervals. The implementation can take advantage of parallelism by forking the recursive calls out to different processors. That presentation, says Lamport, describes only a possible implementation. The true Quicksort is more general. The algorithm works on a set not_sorted of integer intervals i..j such that the corresponding array slices a [i..j] are the only ones possibly not sorted; the goal of the algorithm is to make not_sorted empty, since then we know the entire array is sorted. In Eiffel we declare this set as:

not_sorted: SET [INTEGER_INTERVAL]

The algorithm initializes not_sorted to contain a single element, the entire interval; at each iteration, it removes an interval from the set, partitions it if that makes sense (i.e. the interval has more than one element), and inserts the resulting two intervals into the set. It ends when not_sorted is empty. Here it is:

……..from                                 — Initialize interval set to contain a single interval, the array’s entire index range:
……..…..create not_sorted.make_one (a.lower |..| a.upper)….         ..……..
……..invariant
……..…..— See below
……..until
……..…..not_sorted.is_empty                                                            — Stop when there are no more intervals in set
……..loop
……..…..picked := not_sorted.item                                                     — Pick an interval from (non-empty) interval set.
……..……if picked.count > 1 then                                                      — (The precondition of partition holds, see below.)
……..……..…..partition (picked.lower, picked.upper)                 — Split, moving small items before & large ones after pivot.
……..……..…..not_sorted.extend (picked.lower |..| pivot)            — Insert new intervals into the set of intervals: first
……..……....…not_sorted.extend (pivot + 1 |..| picked.upper)     — and second.
……..……end
……..…...not_sorted.remove (picked)                                               — Remove interval that was just partitioned.
…….end

Eiffel note: the function yielding an integer interval is declared in the library class INTEGER using the operator |..| (rather than just  ..).

The query item from SET, with the precondition not is_empty,  returns an element of the set. It does not matter which element. In accordance with the Command-Query Separation principle, calling item does not modify the set; to remove the element you have to use the command remove. The command extend adds an element to the set.

The abstract idea behind Lampsort, explaining why it works at all, is the following loop invariant (see [2] for a more general discussion of how invariants provide the basis for understanding loop algorithms). We call “slice” of an array a non-empty contiguous sub-array; for adjacent slices we may talk of concatenation; also, for slices s and t,  s <= t means that every element of s is less than or equal to every element of t. The invariant is:

a is the concatenation of the members of a set slices of disjoint slices, such that:
– The elements of a are a permutation of its original elements.
– The index range of any member  of slices having more than one element is in not_sorted.
– For any adjacent slices s and t (with s before t), s <= t.

The first condition (conservation of the elements modulo permutation) is a property of partition, the only operation that can modify the array. The rest of the invariant is true after initialization (from clause) with slices made of a single slice, the full array. The loop body maintains it since it either removes a one-element interval from not_sorted (slices loses the corresponding slice) or performs partition with the effect of partitioning one slice into two adjacent ones satisfying s <= t, whose intervals replace the original one in not_sorted. On exit, not_sorted is empty, so slices is a set of one-element slices, each less than or equal to the next, ensuring that the array is sorted.

The invariant also ensures that the call to partition satisfies that routine’s precondition.

The Lampsort algorithm is a simple loop; it does not use recursion, but relies on an interesting data structure, a set of intervals. It is not significantly longer or more difficult to understand than the traditional recursive version

sort (i, j: INTEGER)
……..require
……..……..i <= j
……..……..i >= a.lower
……..……..j <= a.upper
……..do
……..……if j > i then                    — Note that precondition of partition holds.
……..……..…..partition (i, j)         — Split into two slices s and t such that s <= t.
……..……..…..sort (i, pivot)          — Recursively sort first slice.
……..……..…..sort (pivot+1, j)      — Recursively sort second slice.
……..……end……..…..
……..end

Lampsort, in its author’s view, captures the true idea of Quicksort; the recursive version, and its parallelized variants, are only examples of possible implementations.

I wrote at the start that the focus of this article is Lampsort as an algorithm, not issues of methodology. Let me, however, give an idea of the underlying methodological debate. Lamport uses this example to emphasize the difference between algorithms and programs, and to criticize the undue attention being devoted to programming languages. He presents Lampsort in a notation which he considers to be at a higher level than programming languages, and it is for him an algorithm rather than a program. Programs will be specific implementations guided in particular by efficiency considerations. One can derive them from higher-level versions (algorithms) through refinement. A refinement process may in particular remove or restrict non-determinism, present in the above version of Lampsort through the query item (whose only official property is that it returns an element of the set).

The worldview underlying the Eiffel method is almost the reverse: treating the whole process of software development as a continuum; unifying the concepts behind activities such as requirements, specification, design, implementation, verification, maintenance and evolution; and working to resolve the remaining differences, rather than magnifying them. Anyone who has worked in both specification and programming knows how similar the issues are. Formal specification languages look remarkably like programming languages; to be usable for significant applications they must meet the same challenges: defining a coherent type system, supporting abstraction, providing good syntax (clear to human readers and parsable by tools), specifying the semantics, offering modular structures, allowing evolution while ensuring compatibility. The same kinds of ideas, such as an object-oriented structure, help on both sides. Eiffel as a language is the notation that attempts to support this seamless, continuous process, providing tools to express both abstract specifications and detailed implementations. One of the principal arguments for this approach is that it supports change and reuse. If everything could be fixed from the start, maybe it could be acceptable to switch notations between specification and implementation. But in practice specifications change and programs change, and a seamless process relying on a single notation makes it possible to go back and forth between levels of abstraction without having to perform repeated translations between levels. (This problem of change is, in my experience, the biggest obstacle to refinement-based approaches. I have never seen a convincing description of how one can accommodate specification changes in such a framework without repeating the whole process. Inheritance, by the way, addresses this matter much better.)

The example of Lampsort in Eiffel suggests that a good language, equipped with the right abstraction mechanisms, can be effective at describing not only final implementations but also abstract algorithms. It does not hurt, of course, that these abstract descriptions can also be executable, at the possible price of non-optimal performance. The transformation to an optimal version can happen entirely within the same method and language.

Quite apart from these discussions of software engineering methodology, Lamport’s elegant version of Quicksort deserves to be known widely.

References

[1] Lamport video here, segment starting at 0:32:34.
[2] Carlo Furia, Bertrand Meyer and Sergey Velder: Loop invariants: Analysis, Classification and Examples, in ACM Computing Surveys, September 2014, preliminary text here.

Our online course Computing: Art, Magic, Science, available from EdX, opens this Tuesday (tomorrow, 30 September) at 9 AM Zurich time (and at this time in your area).

An earlier article on this blog described the course, which integrates ten years of experience teaching introductory programming at ETH, and takes advantage of remote-compilation and remote-execution technology from our distributed development research.

You can find the course here.

The Paris computer science bookstore Le Monde en Tique is organizing, this coming Friday, Oct. 3, starting at 5 PM, a signing session for my book Agile! The Good, the Hype and the Ugly [1].

About the book (for readers new to this site): it provides a cold-blooded analysis of agile methods and examines their claims, their value and their limitations.

Le Monde en Tique is well known to technology aficionados in Paris and far beyond. Jean Demétreaux and his team established it at a time when it was hard, slow and expensive to order technical books from international publishers. While other legendary bookstores such a Stacey’s in San Francisco had to close in response to competition from chain stores and Internet offerings, le Monde en Tique (a pun on “tique” words such as informatics and bureautics, and also on ICT, in French TIC) has found new markets and lives on. It is set in a historic building in the medieval heart of Paris [2]. They already organized such book signings for the publication of the French translation of Object-Oriented Software Construction [3] and of Touch of Class, the latter reported in this blog [4]. If you are nearby, please come on Friday!

References

[1] Bertrand Meyer: Agile! The Good, the Hype and the Ugly, Springer, 2014,  Amazon page: here, book page: here.

[2] Book signing announcement with access instructions: here.

[3] Bertrand Meyer: Conception et Programmation Orientées Objet (translation of Object-Oriented Software Construction, 2nd edition, Prentice Hall), Eyrolles, Paris 2008, book page here.

[4] Knuth and Company, article on this blog, 19 October 2009, see here.

The IEEE’s Harlan Mills award is the principal prize in software engineering. The 2014 recipients are Patrick and Radhia Cousot, recognized for their groundbreaking work on abstract interpretation; Patrick will receive the award at ICSME 2014 on Oct. 1st. The list of previous recipients is here.

I have the privilege of serving as the current committee chair; the deadline for nomination is October 15. Please nominate your favorite software engineering grandee! You can find more information and the nomination form here.

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I have temporarily withdrawn this article because the specific case it used as an example has changed. I will re-publish it as soon as the situation has stabilized.