It's a parable which means it is fiction that that ignores details to make a point. As such it does it's job quite well unless you yet to read more into it than the author intended.
To me this says that parables are fairly useless: with enough padding any trivial insight may seem wise. I can't at the moment imagine something that I would think important to communicate which would be made more clear by a parable. I would also be concerned about being patronizing. I'm sure this makes good fodder for academic quibbling, but I am beginning to doubt whether Dijkstra was more insightful than arrogant.
Re:A Parable by Dijkstra (1973)
by dredmorbius on Monday July 16, 2018 @12:56PM
(#17542795)
All metaphors melt if you push them loudly enough.
Rolling stock needs maintenance, and if you keep units permanently paired you can easily run out of units.
In fact there is no easy solution given realistic business constraints. You can either put toilets in every car, which has a cost because it reduces available seating. In the best case you’ll lose money because of the lost seats. In the worst case overcrowding will make the toilets ineffective.
Or you can buy enough spare units to allow for maintenance, which has a larger up front cost, and continuing costs in terms of stabling, and possible issues with shunting yard size.
Working out the most efficient answer given real trains, real passenger loads, likely future passenger loads, and shunting yard constraints, is not a trivial problem.
Unlike Dijkstra, some of the managers in his audiences will have understood this. It’s no wonder they found his glib hand-waving annoying.
The actual lesson of the parable is the opposite of the one Dijkstra is making: the real world is hard, and if you think a solution fits neatly into a trivial software construct, you’re almost certainly wrong.