The UDC, in some ways, seems very similar to Ranganathan’s colon classification system, as it allows more extended classification of items than is possible in the Dewey Decimal System, which makes it much more flexible. I wonder why it is that the UDC has become so popular and widespread while colon classification doesn’t seem to be widely used? In the article by Alex Wright, he mentions that the UDC has been translated into 30+ languages, so that seems to be a big factor there. I guess also Ranganathan’s system seemed to be much more theoretical than the UDC. However, as mentioned in the Rayward article, Otlet also ran into some issues with shelving, which is a problem for colon classification as well.
It’s very impressive to read about the amount that Otlet was able to accomplish, and it’s awful that so much of what he did was destroyed after he devoted decades to it. At least the UDC itself survived, even if Otlet’s Mundaneum did not.