I wasn't asserting that they were pervasive or even universal (in the Unix universe). Perhaps I'm missing your point about dbm, unless it's just that libraries

I wasn't asserting that they were pervasive or even universal (in the Unix universe). Perhaps I'm missing your point about dbm, unless it's just that libraries existed, even long ago, that happened to open files. That doesn't refute my point, which is that a process operating on those files via that library and outside of that library is incongruous. As further evidence for there being at least an idea of such a dual "class" of files, I present the fact that the * glob does not match files starting with a dot.