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Table of contents
The software crisis was due to the rapid increases in computer power and the complexity of the problems that could be tackled. With the increase in the complexity of the software , many software problems arose because existing methods were insufficient. To put it quite bluntly: as long as there were no machines, programming was no problem at all; when we had a few weak computers, programming became a mild problem, and now we have gigantic computers, programming has become an equally gigantic problem.
While Dijkstra had programmed extensively in machine code in the s, he came to the conclusion that in high-level languages frequent use of the GOTO statement was usually symptomatic of poor structure. Dijkstra argued that the programming statement GOTO, found in many high-level programming languages, is a major source of errors, and should therefore be eliminated.
This letter caused a huge debate in the programming community. Some went to the length of equating good programming with the elimination of GO TO. The debate has long since died down; programming languages provide alternatives to the GO TO, few programmers today use it liberally, and most never use it at all. Dijkstra's thesis was that departures from linear control flow were clearer if allowed only in disciplined higher-level structures such as the if-then-else statement and the while loop.
This methodology was developed into structured programming movement , the title of his book, coauthored with C. Hoare and Ole-Johan Dahl. Considered by many as the first significant movement in history of computer programming, structured programming became the new programming orthodoxy during the s. Structured programming is often regarded as "goto-less programming". But as Bertrand Meyer notes, "As the first book on the topic [ Structured Programming by Dijkstra, Dahl, and Hoare] shows, structured programming is about much more than control structures and the goto.
Its principal message is that programming should be considered a scientific discipline based on mathematical rigor. Dijkstra's Structured Programming article precipitated a decade of intense focus on programming techniques that has fundamentally altered human expectations and achievements in software development.
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Before this decade of intense focus, programming was regarded as a private, puzzle-solving activity of writing computer instructions to work as a program. After this decade, programming could be regarded as a public, mathematics-based activity of restructuring specifications into programs.
Before, the challenge was in getting programs to run at all, and then in getting them further debugged to do the right things. After, programs could be expected to both run and do the right things with little or no debugging. Before, it was common wisdom that no sizable program could be error-free. After, many sizable programs have run a year or more with no errors detected. These expectations and achievements are not universal because of the inertia of industrial practices. But they are well-enough established to herald fundamental change in software development. Reilly, notes that "the major contributions of structured programming have been twofold—the elevation of programming technique to something less of an art and more of a science, and the demonstration that carefully structured programs can be creative works of sufficient literary merit to deserve being read by humans and not just by computer.
Dijkstra's ideas about programming methodology especially the structured programming movement helped lay the foundations for the birth and development of the professional discipline of software engineering in particular the software design and development , enabling programmers to organize and manage increasingly complex software projects. And in the mid s David Parnas and others clarified the idea and showed how to apply it in software engineering principles. The rise of the structured programming movement led to many other structured approaches applied to software design.
The techniques of structured analysis and structured design are outgrowths of structured programming concepts and techniques, and of the early ideas about modular design. Principles of modularity were strengthened by Larry Constantine 's concepts of coupling to be minimized between modules and cohesion to be maximized within modules , by David Parnas 's techniques of information hiding , and by abstract data types.
The field of software metrics is often considered as a direct influence of the structured programming movement on software engineering in the s. Separation of concerns SoC , one of the basic principles in software engineering , is a design principle for separating a computer program into distinct sections, such that each section addresses a separate concern. The term separation of concerns was coined by Dijkstra in his paper "On the role of scientific thought".
In the s Dijkstra and his colleagues in Eindhoven designed and implemented THE standing for ' Technische Hogeschool Eindhoven ' operating system , which was organised into clearly identified layers. Prior to this paper, engineers had struggled with the problem of how to organize software. If you look at early examples of programs, and you can find many in the electronic library of the Computer Society, you will find that most code of that era is complicated, difficult to read, hard to modify, and challenging to reuse. In his paper, Dijkstra described how software could be constructed in layers and gave an example of a simple operating system that used five layers.
He admitted that this system might not be a realistic test of his ideas but he argued that the "larger the project, the more essential the structuring!
We see it in many forms and apply it to many problems. We see it in the hierarchy of classes in object-oriented programming and in the structure of Service-Oriented Architecture SOA. SOA is a relatively recent application of layering in computer science. It was articulated in as a means of controlling complexity in business systems, especially distributed systems that make substantial use of the Internet. The S3's nine layers are: 1 operational systems, 2 service components, 3 services, 4 business processes, 5 consumer actions, 6 system integration, 7 quality control and assurance, 8 information architecture, and 9 system governance and policies.
Dijkstra organized the design of the system in layers in order to reduce the overall complexity of the software. Though the term 'architecture' had not yet been used to describe software design , this was certainly considered the first glimpse of software architecture. By way of introduction, the Editor-in-Chief says, "This project initiated a long line of research in multilevel systems architecture — a line that continues to the present day because hierarchical modularity is a powerful approach to organizing large systems.
In a one-page paper from Dijkstra introduced the ' mutual exclusion problem' for n processes and discussed a solution to it. It was probably the first published concurrent algorithm. Per Brinch Hansen , a pioneer in the field of concurrent computing , considers Dijkstra's Cooperating Sequential Processes to be the first classic paper in concurrent programming. As Brinch Hansen notes, 'Dijkstra lays the conceptual foundation for abstract concurrent programming' with that paper. In Dijkstra published his seminal paper ' Cooperating sequential processes ', a page essay that originated the field of concurrent programming.
He discussed in it the notion of mutual exclusion mutex and the criteria a satisfactory solution should satisfy. He also redressed the historical perspective left out of his paper by including the first known correct solution to the mutual exclusion problem , for two processes, due to Theodorus Dekker. Dijkstra subsequently generalized Dekker's solution to n processes. He also identified the ' deadlock problem' called there 'the problem of the deadly embrace '  and proposed an elegant ' Banker's algorithm ' that prevents deadlock.
The deadlock detection and prevention became perennial research problems in the field of concurrent programming. The dining philosophers problem is an example problem often used in concurrent algorithm design to illustrate synchronization issues and techniques for resolving them. It was originally formulated in by Dijkstra as a student exam exercise, presented in terms of computers competing for access to tape drive peripherals. Soon after, Tony Hoare gave the problem its present formulation. Dijkstra , who introduced the mutual exclusion problem, the concept of a process, the semaphore object, the notion of a weakest precondition , and guarded commands among many other contributions , synchronization is no longer a catalog of tricks but a domain of computing science with its own concepts, mechanisms, and techniques whose results can be applied in many domains.
This means that process synchronization has to be a major topic of any computer science curriculum. John W. McCormick et al. Implementation of parallelism is a topic in computer systems hardware and software that is essentially independent of concurrent programming. Concurrent programming is important because it provides an abstract setting in which to study parallelism without getting bogged down in the implementation details.
Dijkstra was one of the very early pioneers of the research on principles of distributed computing. Dijkstra's paper, Solution of a Problem in Concurrent Programming Control was the first to present the correct solution to the mutual exclusion problem. Leslie Lamport writes that this work "is probably why PODC exists" and it "started the field of concurrent and distributed algorithms ". In particular, his paper "Self-stabilizing Systems in Spite of Distributed Control" started the sub-field of self-stabilization.
It is also considered as the first scientific examination of fault-tolerant systems. In his report on Dijkstra's work on self-stabilizing distributed systems , Lamport regard it to be 'a milestone in work on fault tolerance ' and 'a very fertile field for research'. From the s, Dijkstra's chief interest was formal verification. In Dijkstra published a seminal book, A Discipline of Programming , which put forward his method of systematic development of programs together with their correctness proofs.
In his exposition he used his ' Guarded Command Language '. The language, with its reliance on non-determinism, the adopted weakest precondition semantics and the proposed development method has had a considerable impact on the field to this day. The refinement calculus , originally proposed by Ralph-Johan Back  and developed by Carroll Morgan ,  is an extension of Dijkstra's weakest precondition calculus , where program statements are modeled as predicate transformers.
In , to add further support to this approach to programming, he published jointly with Wim Feijen an introductory textbook for first-year students of computer science. The book, first published in Dutch, was entitled Een methode van programmeren. The English edition appeared in as A Method of Programming. Many of his opinions on computer science and programming have become widespread. For example, the programming phrase "two or more, use a for" a rule of thumb when to use a loop is sometimes attributed to him.
He was the first to make the claim that programming is so inherently complex that, in order to manage it successfully, programmers need to harness every trick and abstraction possible. Dijkstra was one of the most famous opponents of the engineering view of computing science. Computer science , as Dijkstra pointed out, deserves a better name.
He suggests it can be called 'computing science'. Instead of the computer, or computing technology, Dijkstra wanted to emphasize the abstract mechanisms that computing science uses to master complexity. When expressing the abstract nature of computing science , he wrote,. A confusion of even longer standing came from the fact that the unprepared included the electronic engineers that were supposed to design, build and maintain the machines.
The job was actually beyond the electronic technology of the day, and, as a result, the question of how to get and keep the physical equipment more or less in working condition became in the early days the all-overriding concern. Quod non [Latin: "Which is not true"].
We now know that electronic technology has no more to contribute to computing than the physical equipment. We now know that programmable computer is no more and no less than an extremely handy device for realizing any conceivable mechanism without changing a single wire, and that the core challenge for computing science is hence a conceptual one, viz. In The Humble Programmer , Dijkstra wrote: "We must not forget that it is not our [computing scientists'] business to make programs, it is our business to design classes of computations that will display a desired behaviour.
Dijkstra also opposed the inclusion of software engineering under the umbrella of academic computer science. He wrote that, "As economics is known as "The Miserable Science", software engineering should be known as "The Doomed Discipline", doomed because it cannot even approach its goal since its goal is self-contradictory.
In the world of computing science, Dijkstra is well known as a "character". In the preface of his book A Discipline of Programming he stated the following: "For the absence of a bibliography I offer neither explanation nor apology. But Dijkstra chose this way of working to preserve his self-reliance. As a university professor for much of his life, Dijkstra saw teaching not just as a required activity but as a serious research endeavor. When lecturing, the long pauses between sentences have often been attributed to the fact that English is not Dijkstra's first language.
However the pauses also served as a way for him to think on his feet and he was regarded as a quick and deep thinker while engaged in the act of lecturing. His courses for students in Austin had little to do with computer science but they dealt with the presentation of mathematical proofs. He never followed a textbook , with the possible exception of his own while it was under preparation. When lecturing, he would write proofs in chalk on a blackboard rather than using overhead foils.
He invited the students to suggest ideas, which he then explored, or refused to explore because they violated some of his tenets. He assigned challenging homework problems, and would study his students' solutions thoroughly. He conducted his final examinations orally, over a whole week. Each student was examined in Dijkstra's office or home, and an exam lasted several hours. He was also highly original in his way of assessing people's capacity for a job.
When Vladimir Lifschitz came to Austin in for a job interview, Dijkstra gave him a puzzle. Vladimir solved it and has been working in Austin since then. Despite having invented much of the technology of software, Dijkstra eschewed the use of computers in his own work for many decades. Even after he succumbed to his UT colleagues' encouragement and acquired a Macintosh computer , he used it only for e-mail and for browsing the World Wide Web. He preferred to rely on his typewriter and later on his Montblanc pen.
He repeatedly tried other pens, but none ever displaced the Montblanc. He had no use for word processors , believing that one should be able to write a letter or article without rough drafts, rewriting, or any significant editing. He would work it all out in his head before putting pen to paper, and once mentioned that when he was a physics student he would solve his homework problems in his head while walking the streets of Leiden. He never had a secretary and took care of all his correspondence alone. Throughout Dijkstra's career, his work was characterized by elegance and economy.
They were essays and parables; fairy tales and warnings; comprehensive explanation and pedagogical pretext.
Most were about mathematics and computer science; others were trip reports that are more revealing about their author than about the people and places visited. It was his habit to copy each paper and circulate it to a small group of colleagues who would copy and forward the papers to another limited group of scientists. He once said he had asked his mother whether trigonometry was a difficult topic. She replied that he must learn all the formulas and that furthermore if he required more than five lines to prove something, he was on the wrong track.
Dijkstra was famous for his wit, eloquence, rudeness, abruptness and often cruelty to fellow professionals, and way with words, such as in his remark, "The question of whether Machines Can Think … is about as relevant as the question of whether Submarines Can Swim. In many of his more humorous essays, Dijkstra described a fictional company of which he served as chairman. The company was called Mathematics, Inc.
He invented a number of activities and challenges of Mathematics Inc. The imaginary company had produced a proof of the Riemann Hypothesis but then had great difficulties collecting royalties from mathematicians who had proved results assuming the Riemann Hypothesis. The proof itself was a trade secret. Dijkstra was well known for his habit of carefully composing manuscripts with his fountain pen.
After going to Eindhoven , Dijkstra experienced a writer's block for more than a year. Dijkstra distributed photocopies of a new EWD among his colleagues. Many recipients photocopied and forwarded their copies, so the EWDs spread throughout the international computer science community. The topics were computer science and mathematics, and included trip reports, letters, and speeches. These short articles span a period of 40 years. Almost all EWDs appearing after were hand-written. They are rarely longer than 15 pages and are consecutively numbered. The last one, No.
More than EWDs have been scanned, with a growing number transcribed to facilitate search, and are available online at the Dijkstra archive of the University of Texas. Dijkstra's self-confidence went together with a remarkably modest lifestyle , to the point of being spartan. An enthusiastic listener of classical music , Dijkstra's favorite composer was Mozart.
Dijkstra died on 6 August According to officials at the University of Texas, the cause of death was cancer. The citation for the award reads: . Edsger Dijkstra was a principal contributor in the late 's to the development of the ALGOL , a high level programming language which has become a model of clarity and mathematical rigor. He is one of the principal exponents of the science and art of programming languages in general, and has greatly contributed to our understanding of their structure, representation, and implementation. His fifteen years of publications extend from theoretical articles on graph theory to basic manuals, expository texts, and philosophical contemplations in the field of programming languages.
The introduction given at the awards ceremony is a tribute to Dijkstra: . The working vocabulary of programmers everywhere is studded with words originated or forcefully promulgated by E. Dijkstra — display, deadly embrace , semaphore, go-to-less programming, structured programming. But his influence on programming is more pervasive than any glossary can possibly indicate. The precious gift that this Turing Award acknowledges is Dijkstra's style: his approach to programming as a high, intellectual challenge; his eloquent insistence and practical demonstration that programs should be composed correctly, not just debugged into correctness ; and his illuminating perception of problems at the foundations of program design.
And at the center of this movement, creating and reflecting patterns no less beautiful than useful, stands E. Edsger is widely recognized as a man who has thought deeply about many deep questions; and among the deepest questions is that of traditional moral philosophy: How is it that a person should live their life? Edsger found his answer to this question early in his life: He decided he would live as an academic scientist, conducting research into a new branch of science, the science of computing.
He would lay the foundations that would establish computing as a rigorous scientific discipline; and in his research and in his teaching and in his writing, he would pursue perfection to the exclusion of all other concerns. From these commitments he never deviated, and that is how he has made to his chosen subject of study the greatest contribution that any one person could make in any one lifetime. In March , the following email was sent to the distributed computing community: .
Dijkstra, a pioneer in the area of distributed computing. His foundational work on concurrency primitives such as the semaphore , concurrency problems such as mutual exclusion and deadlock , reasoning about concurrent systems, and self-stabilization comprises one of the most important supports upon which the field of distributed computing is built.
No other individual has had a larger influence on research in principles of distributed computing. Denning wrote about Dijkstra: . Edsger Dijkstra, one of the giants of our field and a passionate believer in the mathematical view of programs and programming Over the previous quarter-century, he had formulated many of the great intellectual challenges of the field as programming—the goto statement, structured programming, concurrent processes, semaphores, deadlocks, recursive programming in Algol, and deriving correct programs. Among Dijkstra's awards and honors are: .
The award was first approved in and the first election was made in to Dijkstra. Speakers came from all over the United States and Europe, and a group of computer scientists contributed research articles which were edited into a book. Beginning in , this award recognizes the top academic performance by a graduating computer science major.
Selection is based on GPA in all major courses and election by department faculty. Dijkstra Memorial Lecture on 12 October This lecture series was made possible by a generous grant from Schlumberger to honor the memory of Dijkstra. From Wikipedia, the free encyclopedia. Edsger Wybe Dijkstra. Rotterdam , Netherlands. Nuenen , Netherlands. Computing science Theoretical computer science Systems science. Adriaan van Wijngaarden. Frana, Communications of the ACM 53 8 , Academic Press. Structured Programming.
A Discipline of Programming. Prentice Hall. Monographs in Computer Science. A Method of Programming. Predicate Calculus and Program Semantics. Texts and Monographs in Computer Science. Numerische Mathematik. IFIP Congress. Amsterdam: North-Holland. Cooperating Sequential Processes. Technische Hogeschool Eindhoven. Reprinted in Genuys, F. Programming Languages: N. Letters to the editor. BIT Numerical Mathematics. ACM Symp. Eindhoven: Technische Hogeschool.
Acta Inform. American Mathematical Monthly. Dijkstra, Edsger W. On the role of scientific thought EWD Dijkstra , pp. ACM Pacific Dijkstra, Edsger W Language Hierarchies and Interfaces. International Computing Symposium. Program Construction. ACM Proceedings of the international conference on Reliable software. The threats to computing science EWD The Mathematical Intelligencer. A debate on teaching computing science. Retrieved 12 August Dijkstra started the field of concurrent and distributed algorithms with his CACM paper "Solution of a Problem in Concurrent Programming Control", in which he first stated and solved the mutual exclusion problem.
That paper is probably why PODC exists; it certainly inspired most of my work. Stepanov Edizioni Infomedia srl. Retrieved 21 December Alexander Stepanov : " I also discovered books of two great computer scientists from whose work I learned the scientific foundation of my trade: Donald Knuth and Edsger Dijkstra. Knuth taught me the answers. Dijkstra taught me the questions.
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Time and time again I come back to their works for new insights. As Brown University 's Sorin Istrail notes, "A prolific writer, he [Dijkstra] authored more than 1, papers, many written by hand in his precise and elegant script. I read them with joy and excitement and my love for mathematics and computer science has been influenced in no small measure by his works. Physics Today. Bibcode : PhT The University of Texas at Austin.
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Retrieved 20 August New York Times. Retrieved 10 April The Guardian. Retrieved 19 April Computing Surveys. As Donald Knuth remarked, "A revolution is taking place in the way we write programs and teach programming, because we are beginning to understand the associated mental processes more deeply. The reason for this revolution and its future prospects have been aptly described by E.
TRIZ Journal. Retrieved 18 August Springer , p. Encyclopedia of Computer Science and Technology , revised edition. Facts on File, Inc. Retrieved 22 September As Leslie Lamport notes, "While concurrent program execution had been considered for years, the computer science of concurrency began with Edsger Dijkstra's seminal paper that introduced the mutual exclusion problem.
The first scientific examination of fault tolerance was Dijkstra's seminal paper on self-stabilization. The ensuing decades have seen a huge growth of interest in concurrency—particularly in distributed systems. The team at Automated finally releases an implementation timetable. In another two months they will have a test version of the program. Then a two month period of testing and enhancing should yield a completed version.
The manager of Charles has by now [become] tired of seeing him goof off. He decides to confront him. He decides to postpone the confrontation, so makes some small talk then leaves. However, he begins to keep a closer watch on Charles, so that when the opportunity presents itself he can confront him. Not looking forward to an unpleasant conversation, he is pleased to notice that Charles seems to be busy most of the time. He has even been seen to delay his lunch, and to stay after work two or three days a week. At the end of three months, Charles announces he has completed the project.
He submits a line program. The program appears to be clearly written, and when tested it does everything required in the specifications. In fact it even has a few additional convenience features which might significantly improve the usability of the program. The program is put into test, and, except for one quickly corrected oversight, performs well. The team at Automated has by now completed two of the four major modules required for their program. These modules are now undergoing testing while the other modules are completed.
After another three weeks, Alan announces that the preliminary version is ready one week ahead of schedule. He supplies a list of the deficiencies that he expects to correct. The program is placed under test. The users find a number of bugs and deficiencies, other than those listed. As Alan explains, this is no surprise. After all this is a preliminary version in which bugs were expected. After about two more months, the team has completed its production version of the program. It consists of about 2, lines of code. When tested it seems to satisfy most of the original specifications.
It has omitted on or two features, and is very fussy about the format of its input data.
Edsger W. Dijkstra - Wikipedia
However the company decides to install the program. They can always train their data-entry staff to enter data in the strict format required. The program is handed over to some maintenance programmers to eventually incorporate the missing features. But as he read through the source code, he realized that the project was really much simpler than he had originally thought.
It now seemed apparent that this was not much of a challenge even for a beginning programmer. Charles did produce about 5 lines of code per day. This is perhaps a little above average. However, considering the simplicity of the program, it was nothing exceptional.