Lexical search retrieves documents by matching exact words or phrases. It is especially valuable when a query contains technical terms, product-taxonomy phrases, API endpoints, or ambiguous words whose precise form matters. section 7.2.4 section 7.2.2
A lexical system can rank matches with Best Matching 25 (BM25), which considers how often a term appears and how distinctive it is across the document collection. This prioritizes useful exact hits instead of returning every document containing the term. section 7.2.4
Use lexical search when:
- A phrase such as “augmented workflow” must refer to one defined feature rather than merely related concepts. section 7.2.4
- Users need exact API endpoints or other company-specific terminology. section 7.2.4
- A word is ambiguous, such as “business” in an airline query, and broad semantic similarity produces irrelevant results. section 7.2.4
Precision plus context
A search for “augmented workflow” may retrieve semantically related material, but lexical matching ensures documents containing that exact taxonomy phrase appear. Combining both approaches preserves semantic context while improving precision. section 7.2.4
Lexical search does not replace semantic search: exact matching can miss documents that use synonyms or related wording. A combined system uses lexical precision alongside semantic recall, with metadata filters as another retrieval optimization. section 7.2.2 section 7.4
