Thursday, 27 August 2009

Tony Hoare and the meaning of life (well, almost...)

You know, I was always wondering about programming - is it an art, a craft, or is it an engineering discipline? Some crazy hackers maintain it be an art, more down-to-earth types oscillate between craft and engineering.

My personal feeling was that it couldn't be engineering - I missed the scientific part of it, it was too "soft". For me software engineering appeared rather to be a set of rules of thumb for organizing our mental work (functions, classes, modules...), something from the realm of cognitive science perhaps :-). For example I couldn't take my multithreading program and prove it not to deadlock in a future (i.e not yet written, but planned) installment of this blog...

1. The presentation

And then, some months ago, I came across that presentation* given on QCon 2009 Conference by Sir C.A.R. Hoare (aka Tony Hoare of the Hoare logic, Quicksort, and CSP fame) about relationships between programming and computer science.

Computer Science is about how programs run and how correct programs can be constructed *
By the way, I used to dislike the all-present video presentations, which seem to be replacing the old-fashioned articles as programmer's information source of choice. Well, to put it frankly, I hated them! Instead of beeing able to quickly scoop the essentials and then read the article if it'd interest me, I'm now forced to hear for hours to some uninspiring presentations and often to some really horrible accents to boot, as to discover that in the end only the title of the video was interesting!

But on the other side, with the video presentations I'm no able to hear people like Linus Thorvald** and Tony Hoare in person, and it proved to be very rewarding to me in both cases. Watching Tony Hoare was a great pleasure - he's a wonderfully gentle and good humored old man, I'd say my idol of sorts. And as he's got his first degree in philosophy, so he's bound to have some interesting insights in the question at hand.

His answer is both simple and compelling (I'm rephrasing it here):
Software Engineering is an engineering discipline because it uses Computer Science, and Computer Science is a science because its results are exploited and confirmed by software products!*
Sounds at first rather convincing, doesn't it? But wait, for a philosophy major, isn't he overlooking something?

2. Circulus Vitiosus?

Well, embarassingly, it's looking suspiciously similiar to a circular argument , right? For SW Engineering gets justified by the CS but the CS is justified by SW Engineering? It certainly appeared like this to me at the first glance So let us have a closer look at it:

science is: "the systematic study of the structure and behaviour of the physical world, especially by watching, measuring and doing experiments, and the development of theories to describe the results of these activities "***
Does this apply here? Well, maybe, if for "physical world" we substitute the human-built things like hardware and binaries. But wait, don't we rather work with mental constructs instead (you know, languages, functions, classes)? Well, yes, but they are models, like math is a model in civil engineering. In the end it's all about how the binary runs!

engineering is: "to design and build something using scientific principles"***
This one seems to fit perfectly. So both parts of the argument are corrct, but it is a circular one? Let it translate it form English into the language of logic:
(CS usedIn SWEng => SWEng is Eng) and (CS usedIn SWEng => CS is Sc)
You see it's not really circular, as it's two separate propositions, and they are just rephrasing the two above definitions (check it!). Because science is defined as a special, rigorous kind of examination of the physical world, and engineering uses science when dealing with this world directly! But wait again, it's not said that we are allowed to use only scince in engineering, or ist it?

3. The Engineer an the Scientist

This leads us to another interesting aspect of that presentation, which was the comparison between science and engineering, and how they relate to each other. Somehow explaining the above realtionship (I must paraphrase again):

so it's first:
scientists are interested in pure truths, i.e. programs which doesn't have errors, while an engineer must compromise, i.e. live with programs that have got some errors,

and second:
scientists are interested in certainity, while an engineer lives in incertanity, must take risks and perform risk management,

and thus:
scientists should be women, engineers should be men (Yes, he really made this little joke:)

There are several other comparisions along these lines in the presentation, and furthermore, even a gradation between the two extremes like applied scientist or scientific engineer are introduced. So there is (almost) a continuum of positions between the two extremes of pure CS scientist an a common hacker.

And that fact harbors some kind of consolation, particularly if I'm in a very pedestrian project and must do the most boring things. Just remember, you can always move up the ladder, and use more science, more absolute truths, and thus (as the ancients believed) come in contact with more beauty. An that's maybe the ultimate "consolatio philosophiae“, or do you think this is an exaggeration on my part?

* all citations are not original but rephrased by yours truly, so if they are wrong it's my fault! Original source: Tony Hoare, "The Science of Computing and the Engineering of Software", QCon Conference, Jun 11, 2009 , London:

** for example this presentation by Linus was fun:

*** the definitions are taken from "Cambridge Advanced Learner's Dictionary", as I was looking for simplicity:


S.P. Sobania said...

I had CSP in school and I liked it much. But that was really the last opportunity I ever had to use it. I wonder why you see so little of it in library designs. For example Scala has actors, but provides nothing even close to CSP. It prefers to treat deadlocks as runtime errors. Same with many other languages.

There is one or two CSP libraries for Java. But they are far from perfection, they simply provide the constructs. There is no validation at runtime, which certainly would be interesting.

Marek Krj said...

@S.P. Sobania

Had a look at the Go language?