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// ⌕ RAG & Vector Retrieval

BM25

Classic keyword ranking by term frequency and rarity.

BM25 关键词检索 2009 Beginner core

Original paper ↓ What to learn first →

IN PLAIN WORDS

Terms frequent in a document but rare in the corpus score high, with saturation and length normalization. Simple yet strong; paired with vectors for hybrid search in RAG.

Used in: Elasticsearch, OpenSearch, hybrid search

01Original paper

The Probabilistic Relevance Framework: BM25 and Beyond

Robertson et al. · Foundations and Trends® in Information Retrieval · 2009

DOI ↗ ✓ Verified · Crossref API doi:10.1561/1500000019

02Where it sits

Learn the left column first; the right column builds on this one.

Learn first

  • No prerequisites — a good starting point
BM25

Then you can learn

  • Nothing in the atlas builds on it yet

Related:Dense Passage Retrieval (DPR)Retrieval-Augmented Generation (RAG)

Dense Passage R…Retrieval-Augme… BM25

Left: prerequisites · right: builds on this · dashed: related. Full map →

03Learning resources

Official docs, explainers, courses and reference code. All links checked.

Reference code

04Where the course teaches it

U80 Embeddings, Vector Search & Reranking BM25, sentence embeddings, DPR, ColBERT, HNSW, PQ and hybrid search. 8 h10 algorithms4 papers

On learning paths:AI Application Engineer

For AI / data

Data updated: AI algorithms & curriculum(UTC+8)