Information Retrieval

BM25 (Best Matching 25) is a probabilistic ranking function that powers modern search engines by scoring document relevance based on query terms, term frequency saturation, inverse document frequency, and document length normalization. As an information retrieval engineer, you’ll use BM25 for precise lexical matching in applications like Elasticsearch, Azure Search, and custom retrievers—outperforming TF-IDF while complementing semantic embeddings in hybrid systems.[1][3][4] This zero-to-hero tutorial takes you from basics to production-ready implementation, pitfalls, tuning, and strategic decisions on when to choose BM25 over vectors or hybrids. ...

Why Most RAG Systems Fail Most Retrieval-Augmented Generation (RAG) systems do not fail because of the LLM. They fail because of bad chunking. If your retrieval results feel: Random Hallucinated Incomplete Loosely related to the query Then your embedding model and vector database are probably fine. Your chunking strategy is the real bottleneck. Chunking determines what the model is allowed to know. If the chunks are wrong, retrieval quality collapses — no matter how good the LLM is. ...