Keywords in Library

I believe it would be really useful for librarians to be able to add keywords (around 5 ?) to the books they write (for example, a book about Sirius Black would have the keywords "animagus", "marauders" and "azkaban"). This system could be enriched with a searching system to search keywords in the whole library (because ctrl + F-ing five books is a big waste of time). 

So when you look for informations about animagus, you type it in the searching bar and you get the book about Sirius, something about Minerva McGonagall, maybe also something about the minister's regulations... Librarians wouldn't have to write tons of books about the same subject and students would find sources way more easily.