The Inverted Index
The data structure behind every search box you have ever used
About 45 minutesMediumThe Internet and Search
What your child can do at the end
Describe an inverted index and its posting lists
The brief
Searching 25 pages by reading all of them is fine. Searching a billion is not. Every search engine solves this the same way: turn the collection inside out. Instead of storing page to words, store word to pages. That single flip is what makes search instant. In this lab you crawl a web, build the index yourself, inspect any word in it, and discover why the index can only rank what it has seen.
Skills it develops
data basicsdecompositionabstraction
How it is assessed
3 graded challenges inside the lab, and 8 questions at the end that check the idea rather than the clicks. Every attempt is saved, so a retry after a mistake counts as the learning it is.