Inverted-Index

• SPLADE

  Sparse Lexical and Expansion Embeddings; learns sparse embeddings compatible with inverted indexes while capturing semantic understanding.

• Sparse Retrieval

  Retrieval using inverted-index term matching and scoring functions like BM25 or TF-IDF; contrasts with dense nearest-neighbour methods.

• DeepImpact

  Learns per-term impact scores for documents using a BERT encoder, enabling semantic-aware scoring with a standard inverted index without query expansion.

• uniCOIL

  Uniform COntextualized Inverted List; assigns a single scalar weight per token using a BERT encoder, bridging dense contextualization and sparse inverted index retrieval.