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Multi-vector retrieval

As explained in AI Agents and Applications

Multi-vector indexing is an indexing technique that associates multiple embedding vectors with each document.

Multi-vector retrieval improves searches that find semantically related but contextually incomplete passages. It associates several embedding vectors with one document, allowing different representations to match the same query while returning a larger synthesis chunk. section 8.4 section 8.8

The usual design has two layers: small retrieval chunks or summaries receive precise embeddings, while larger synthesis chunks remain available for the language model. Matching a lower-layer vector retrieves its linked upper-layer content. section 8.4

A practical implementation follows this sequence:

  • Query the MultiVectorRetriever so a focused match expands into the larger linked document. section 8.4.3

Summary embeddings for travel content

For destination pages, embed summaries of coarse chunks and retrieve the corresponding larger chunks. A direct search over summaries returns concise, focused text; multi-vector retrieval returns broader context that is more useful for answer synthesis. section 8.4.3

How AI Agents and Applications covers it

How deep it goes
Explains the two-layer design, ingestion workflow, retriever setup, and summary-search trade-off without detailing embedding internals.
Examples
Uses travel-destination summaries, Cornwall queries, coarse chunks, linked documents, and a summary-versus-context retrieval comparison.
What you can do after
Build it from scratch with LangChain’s MultiVectorRetriever, a vector store, a byte store, chunk summaries, and linked identifiers.
How it connects
Connects vector search with document chunking, parent-child indexing, RAG, and answer synthesis.

Related concepts

This explainer was generated by Manning's knowledge graph from the text of AI Agents and Applications. The section links point to the parts of the book it draws on.