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Technical implementation · AI Search Infrastructure

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Definition

Dense retrieval is a method of information retrieval that uses neural network-generated embeddings to find semantically relevant content — as opposed to sparse retrieval, which matches based on keyword frequency. Dense retrieval systems compare vector representations of queries and documents to identify meaning-based matches. Dense retrieval is the engine behind modern AI search. When Perplexity or Google AI Overviews retrieve content to ground their answers, they are using dense retrieval systems — not keyword search. Content that is semantically rich, covers a topic’s full conceptual territory, and uses the language of the domain performs better in dense retrieval than content optimized for keyword repetition.

Embedding

Cosine similarity

Sparse retrieval

RAG

Semantic search

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