Flowcharts of programming language constructs
The Nassi-Shneiderman diagram is one way of representing structured program flow by dividing up a two-dimensional area. It can&#x27;t represent unstructured gotos and exceptions, though.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Nassi–Shneiderman_diagram" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Nassi–Shneiderman_diag...</a><p>&gt;A Nassi–Shneiderman diagram (NSD) in computer programming is a graphical design representation for structured programming. This type of diagram was developed in 1972 by Isaac Nassi and Ben Shneiderman who were both graduate students at Stony Brook University. These diagrams are also called structograms, as they show a program&#x27;s structures.<p>&gt;Overview: Following a top-down design, the problem at hand is reduced into smaller and smaller subproblems, until only simple statements and control flow constructs remain. Nassi–Shneiderman diagrams reflect this top-down decomposition in a straightforward way, using nested boxes to represent subproblems. Consistent with the philosophy of structured programming, Nassi–Shneiderman diagrams have no representation for a GOTO statement.<p>&gt;Nassi–Shneiderman diagrams are only rarely used for formal programming. Their abstraction level is close to structured program code and modifications require the whole diagram to be redrawn, but graphic editors removed that limitation. They clarify algorithms and high-level designs, which make them useful in teaching. They were included in Microsoft Visio and dozens of other software tools, such as the German EasyCode.<p>&gt;In Germany, Nassi–Shneiderman diagrams were standardised in 1985 as DIN 66261. They are still used in German introductions to programming, for example Böttcher and Kneißl&#x27;s introduction to C, Baeumle-Courth and Schmidt&#x27;s introduction to C and Kirch&#x27;s introduction to C#.<p>&gt;Nassi–Shneiderman diagrams can also be used in technical writing.<p>When Ben Shneiderman and Ike Nassi (who were grad students at the time) submitted their paper about them to Communications of the ACM, it was quickly rejected on October 4, 1972, with the most brutal rejection letter Ben Shneiderman has ever received.<p>But then they submitted it to the unrefereed ACM SIGPLAN, where it was published in August 1973, and since then it has been cited many times, widely implemented by many tools, and used for educational and documentation purposes. It&#x27;s a great example of the importance of persistence for people whose new ideas are brutally rejected by respected authorities:<p>Flowchart techniques for structured programming:<p><a href="https:&#x2F;&#x2F;dl.acm.org&#x2F;doi&#x2F;10.1145&#x2F;953349.953350" rel="nofollow">https:&#x2F;&#x2F;dl.acm.org&#x2F;doi&#x2F;10.1145&#x2F;953349.953350</a><p>Scan of the brutal referee&#x27;s report:<p><a href="https:&#x2F;&#x2F;www.cs.umd.edu&#x2F;hcil&#x2F;members&#x2F;bshneiderman&#x2F;nsd&#x2F;rejection_letter.pdf" rel="nofollow">https:&#x2F;&#x2F;www.cs.umd.edu&#x2F;hcil&#x2F;members&#x2F;bshneiderman&#x2F;nsd&#x2F;rejecti...</a><p>&gt;My first thought was to write a referees report which would by its sarcastic nature be funny. For example, I thought of writing that it was a sound, useful theory, but it wasn&#x27;t practical because it would be difficult to design flowcharting templates to be manufactured and sold.<p>&gt;I guess, however, that it is best to come right out and say that I feel the best thing the authors could do is collect all copies of this technical report and burn them, before anybody reads them. My opinion is that it shows the inexperience and ignorance of the authors with respect to programming in general, and their misunderstanding of so-called structured programming.<p>&gt;To say that [BEGIN body END] should be written as [NS diagram] is ridiculous. Even more ridiculous is having to write [DO i=1 TO N; DO J=1 TO N; S = 0; DO K=1 TO N; S=S+A(I,K)*B(K,J) END C(I,J)=S END END] as [NS diagram].<p>&gt;The authors mention that &quot;the ease with which a structured flow-chart can be translated into a structured program is pleasantly surprising&quot;. My retort is &quot;yes, just erase those silly boxes!&quot;<p>&gt;Flowcharts are a crutch we have invented to try to understand programs written in a confusing style. This was due to our ignorance of the programming process and what was needed -- after all, programming is only 20-30 years old. So-called &quot;structured programming&quot; helps to limit us to, as Dijkstra calls them, &quot;intellectually manageable&quot; programs, in which case flowcharts are completely useless and in fact a hindrance to programming. They shouldn&#x27;t be used.<p>&gt;I shudder at the thought of further explorations revolving around the context-free nature of this [flowchart] language.<p>Ben&#x27;s rejection letter story:<p><a href="https:&#x2F;&#x2F;www.cs.umd.edu&#x2F;hcil&#x2F;members&#x2F;bshneiderman&#x2F;nsd&#x2F;rejection_letter.html" rel="nofollow">https:&#x2F;&#x2F;www.cs.umd.edu&#x2F;hcil&#x2F;members&#x2F;bshneiderman&#x2F;nsd&#x2F;rejecti...</a><p>&gt;Rejection letter from the Communications of the ACM<p>&gt;Ben Shneiderman, June 12, 2003<p>&gt;Our submission of the structured flowcharts to the Communications of the ACM was quickly rejected, on October 4, 1972, by the Programming Languages Editor David Gries of Cornell University. He included a single anonymous reference letter which is on paper that has a Cornell University watermark. I assume Gries gave our paper to one of his colleagues (you can play the guessing game too), who wrote the most brutal rejection letter I have ever gotten.<p>&gt;The reviewer wrote: &quot;I feel that the best thing the authors could do is collect all copies of this technical report and burn them, before anybody reads them.&quot; As graduate students, this stinging rejection shocked us, but we kept getting enthusiastic responses from people around us. We sent the paper to the unrefereed ACM SIGPLAN Notices, where it was published in August 1973. It didn&#x27;t take long for others to produce extensions, software tools, and applications of structured flowcharts.<p>&gt;The next problem was theft of the idea. I had sent a draft to respected colleagues, and soon others published slight variations. One of these respected colleagues was Ned Chapin, who greatly troubled us by publishing what he called &#x27;Chapin Charts.&#x27; A friend of mine sent me his published paper with a note encouraging me to sue. For several years I feared that Chapin&#x27;s reputation and his frequent professional seminars would wind up leaving the idea tied to his name, but as the decades passed, the ending has proved to be a happy one. We called the idea &#x27;structured flowcharts, but they are widely known as Nassi-Shneiderman Diagrams.<p>&gt;Another problem was the appearances of patents for variations on our idea, but these have not limited the widespread recognition we have gotten over the years.<p>&gt;I wish every graduate student or young inventor would have the pleasure of seeing his&#x2F;her ideas spread so far and influence the work of so many people. I also hope that the story of the bold rejection of our novel idea and its eventual international success, is an inspiration for anyone whose new ideas are rejected by some respected authorities.<p>More on Ben Shneiderman and NS diagrams:<p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11368430" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11368430</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11370099" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11370099</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=22093072" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=22093072</a>