Lexical Search - Keyword / Full Text Search
Text Preprocessing / Stemming / Normalization
Ranking Functions
TF-IDF
BM25
Indexing
Inverted Index
Production Systems
Lucene
ElasticSearch
Semantic / Neural Search
Embedding Methods
BERT
ModernBERT
Neural Retrieval
Two Tower / Bi-Encoder
Cross Encoders
Late Interaction Models
ColBERT
Vector Search
Hybrid Methods
SPLADE - Sparse Lexical and Expansion Model for First Stage Ranking
Query - Understanding, Expansion, Parsing
Learning to Rank (LTR)
Models
GBDT - Gradient Boosted Decision Trees
LambdaRank
LambdaMART
Linear Models - Logistic Regression
Neural Methods
Ranking Types
Pointwise
Pairwise
Listwise
Ranking Signals
Data
Synthetic Data
Documents ⇒ LLM Generated Queries ⇒ Retrieved Documents ⇒ LLM Relevance Ranking / Judgment
Query Lists + Results ⇒ LLM as Judge Scoring
Hard Negative Mining
Document / Index Expansion
Datasets
Evaluation
Links