[Retrieval](https://js.langchain.com/docs/concepts/retrieval/): LLM should read this page when (seeking to understand different retrieval systems, implementing query analysis techniques, or building a RAG application) (Comprehensive guide on retrieval systems that covers key concepts like query analysis and information retrieval. Explains techniques for query re-writing and construction, and details various retrieval systems including lexical search indexes, vector indexes, relational databases, and graph databases. Provides implementation examples for specific approaches like decomposition, step-back prompting, HyDE, and self-query retrieval.)

