JSYK, as a (former) librarian for over seven years, I have to tell you that I absolutely ABHORE the Dewey Decimal system.

Now, the main classification tree. Totally fine. But then we get into how it classifies things and it just absolutely sucks. It had a complete western-centric bias.

For example: the 200 section (Religion) is mostly Christian-related, from 240 until 289. Islam, Hinduism, etc have only one number each. Every other religion on this planet is crammed into 290-99. In 800 (Literature) 810 until 889 is US and European Literature, with all other languages crammed into 890-99. A similar pattern happens in Language, where English is from 420-29, but Hindi, Arabic, Bengali, Chinese are crammed into Other under 490.

In 900 (History), the USA has from 973-79, each individual number assigned to a region of the United States. No other country has such subdivisions under History.

The DDC is the most widely used classification in the world, and wow, it actually sucks balls.