On the other hand, the Dewey Decimal Classification system was designed in the late 19th Century before modern advances in science and engineering; it originally sort of spread all knowledge evenly around. After this, the sub-classes have gradually been increased until "629 Applied Science (aka Technology) - Other branches of Engineering" includes most of what the modern world uses. You know, computers, cars, aka modern technology etc. etc. This means that you need some very long numerical additions to differentiate between things. Try 629.22199982988. Guess what? Some of these are so meaningless that they now rival Ranganathan for incomprehensibility. In an effort to actually assist the punter in finding, say a car manual for a particular make of car; modern information scientists (sic) have resorted to using the first three letters of the make in order to help.
Of course, in modern libraries, whole number groups have been hunted down, rounded up and sold off in order to pay for internet access, making the whole classification system redundant*. Yee hi There was a secondary purpose. This was to enable vast areas of space to be turned into internet cafes, drop-in and drop-dead (deadbeats and old fogies like me) centres. Dewey is still used.
*I went into what was a reasonably major library a while back - I worked there in the 70s. It now resembles a slightly seedy community centre with a few oversized women and blokes with ponytails and glasses pretending to be experts in finding information on the internet. There are a few shelves of books, all leaning drunkenly into each other, dog-eared and looking slightly defeated like the staff...
Dun't need none of that book lernin.Just as well. You won't find it in a modern British public library.