ClassroomThe classroom
Back to the lesson libraryMECHANISM · 14 MIN
M26.1 CONNECT THE MECHANISM

Find documents through an index of their words

How does a search box find the right page among millions in a blink? Build a tiny search engine, score it with BM25, and watch where word matching breaks.

LESSON OVERVIEW14 min lesson

Lesson overview

How does a search box find the right page among millions in a blink? Build a tiny search engine, score it with BM25, and watch where word matching breaks.

What you’ll explore

  • Lexical retrieval uses indexed terms and ranking functions to find candidate documents; token normalization, document statistics, and query intent determine matching behavior.
GO TO THE SOURCE

Original explanations, connected to the research.

Introduction to Information Retrieval — authors’ online editionThe Probabilistic Relevance Framework: BM25 and Beyond (Robertson & Zaragoza, 2009)BEIR: A Heterogeneous Benchmark for Zero-shot Evaluation of Information Retrieval Models (Thakur et al., 2021)
Suggest a correction

A precise note can make an explanation better.

Choose the scene and describe what needs attention. Download a feedback file to share through a channel you already use. This page does not send feedback or connect you with a reviewer.

The file includes this note, the scene title, and lesson metadata. Your saved progress and quiz responses are excluded. Download before leaving or reloading to keep your note.