E. Dijkstra "Programming considered as a human activity"       

ACM Classic Books Series  
Classics in software engineering book contents
Pages: 1 - 9  
Year of Publication: 1979
ISBN:0-917072-14-6 

REVIEW

When looking back on any kind of movement or revolution, one always likes to point to a beginning: "It began right there --- it all started with so-and-so's famous speech . . . . "

If structured programming can be thought of as a revolution, then surely Dijkstra's landmark paper, "Programming Considered as a Human Activity," published in 1965, marks its beginning. Virtually the entire gospel of structured programming is contained in a few short pages: the arguments against goto statements, the notion of top-down design, the emphasis on program correctness and quality (or "elegance," as Dijkstra prefers to call it), and the strong argument against programs that modify themselves.

In addition to these fundamental concepts, there are some rather classic phrases that first appeared in this paper, and that have popped up in dozens of subsequent articles and books. For example, when discussing the "divide and conquer" approach characterizing top-down design, Dijkstra admits, "I have only a very small head, and must live with it." What seems obvious to us today was a rather novel idea in 1965: the idea that while computers were --- and still are --- getting faster and more powerful, human beings weren't. This theme is repeated again and again, and is essentially the entire subject matter of Dijkstra's 1972 speech, "The Humble Programmer" [included as Paper 10 in this collection].

It is in the 1965 paper, which you are about to read, that Dijkstra suggests that "the quality of . . . programmers was inversely proportional to the density of goto statements in their programs." And, it is in this early paper as well that Dijkstra recounts programming experiments identical to the ones that converted most of the rest of us to structured programming over the next several years: He rewrote unstructured programs into equivalent structured programs, and marvelled at the increase in clarity.

After reading all the pearls of wisdom that are contained in this one paper, one might well ask why the programming industry wasn't converted at once. The answer, I think, has to do with timing and packaging. In 1965, most programmers (and their managers) felt that they had far more serious problems to worry about than eliminating goto statements" After all, IBM had just unleashed the 360 upon the world, and whole armies of people began trying to upgrade from Autocoder to RPG --- that is, /f they could get the hardware and the operating system to work! Programmers spent most of their time trying to figure out how to use more gotos, not fewer --- in the hopes that doing so would help them fit some ponderous accounting application into an 8K machine!

Another reason for slow adoption of the methods was a factor as well of the medium in which the message was presented --- the IFIP Conference, which might be loosely thought of as the international version of the National Computer Conference. Prestigious and scholarly, to be sure, but its published papers attract a considerably smaller reading audience (at least in ~ the United States) than, say, ComputerworM or Datamation. Perhaps the only reason it attracted any American attention at all was that the IFIP Conference was held in New York City that year --- in contrast to the 1971 Conference, which was held in Ljubljana, Yugoslavia!

An additional problem preventing widespread conversion was with the language itself! Introductory quotations came from scientists Ludwig Boltzmann and George Boole, names with which the average programmer is unlikely to be acquainted. Examples chosen in support of the concepts involved prime factors of a twenty-digit number --- not a subject of intense interest to many programmers. Discussions in support of structured programming dealt with the features of ALGOL 60, well known to American programmers as one of their least popular languages. In short, it's a wonder anyone read the paper at all!

But once you do read it, you can see why Dijkstra has the reputation he does. His writing is succinct and yet convincing. Reading Dijkstra, someone said, has been compared to eating marzipan --- it's best to take very small bites, chew slowly, and digest the mouthful before moving on to the next bite.
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