Dijkstra contributed greatly to introducing hierarchical systems into computing. Already in his very first report of 1953 as employee of the Mathematical Centre in Amsterdam, Dijkstra introduced what he would later call separate levels of concern . In 1959–60, he acquired fame after reformulating the problem of ALGOL translation as an hierarchical problem. His intermediate machine-independent stack-based language was, in hindsight, a precursor to the now widely used virtual machine; see chapter 3 in my book The Dawn of Software Engineering .
Some former colleagues of Dijkstra have stressed in interviews with me that Dijkstra was not an engineer (in accordance with their definition of the term). By discussing Dijkstra's characteristic top-down design perspective in my previous post, I have already given one reason why Dijkstra was perceived as a non-engineer. Below I present another reason. While doing so we will again encounter the dichotomy between performance and generality, a dichotomy which Dijkstra seems to have stressed throughout his whole career.
Roughly 80 participants from 15 countries participated in the 1971 summer school in Marktoberdorf. According to Dijkstra, some participants were very theoretically inclined, others more practically minded. Viewed from the present day, the following list of speakers at that summer school is impressive. Dijkstra attributed a theme to each speaker, with the exception of Perlis and Dahl:
The T.H.E. multiprogramming system — as designed and implemented by Dijkstra, Bron, Habermann, Hendriks, Ligtmans, and Voorhoeve — was studied by Mike McKeag during his visit to Eindhoven some time during the first half of 1971. Subsequently, McKeag went back to his university in Belfast (in Hoare's research group) where he wrote a report of the T.H.E. system. That report was sent to Dijkstra on 22 July 1971 with a cover letter stating:
Dijkstra visited the USA several times before moving to Texas in 1984. In the summer of 1971, he went on a trip to the USA and Canada. It wasn't his first trip to North America, but it was the first time his wife Ria accompanied him. The corresponding trip report was written by Dijkstra on June 23rd, 1971 in EWD312.
David N. Freeman, director of Computing Activities at the University of Pennsylvania, contacted Dijkstra in order to express his interest in taking a sabbatical leave at Eindhoven between September 1972 and September 1973. As future posts on this blog will show, he was not the only one to do so. In fact, several American researchers in computing wanted to visit the Netherlands and Eindhoven in particular. Presumably, this was due to Dijkstra's presence at the University of Eindhoven.
Dijkstra wrote a report in Dutch about his trip to Warwick (England), which took place right before Easter, 1971. The purpose of his trip was to attend an IFIP Working Group 2.3 meeting at Warwick University. Some points in Dijkstra's trip report are of general interest: