relevance
3 free lessons tagged relevance across Computer Science, Business. Each one is a short sequence of focused steps with narration and a five-question quiz at the end — take them in any order, no signup required.
Measuring Relevance: Judgments, NDCG, and the Click Trap
Search quality arguments end when there is a number, and begin again over whether the number is honest. This lesson builds offline evaluation from its atoms: a judgment set, precision and recall at k, MRR for known-item queries, and NDCG computed by hand for graded relevance. Then the online half: clicks, position bias, and why the top result gets clicked even when it is wrong.
BM25: How Lexical Relevance Is Actually Computed
Matching finds candidates; scoring orders them, and the ordering is the product. This lesson builds BM25, the default ranking function of Lucene, Elasticsearch and OpenSearch, from its three ingredients: rare terms count more, repeated terms saturate, and long documents get discounted. With the formula, the two tuning knobs, and the saturation curve computed by hand.
Why one page beats another
Thousands of pages match your query; the engine picks ten and orders them. Learn the four questions ranking answers, why links became a proxy for trust, what PageRank actually measured, how the query itself is interpreted before anything is scored, and why chasing individual ranking factors is the wrong mental model.