Adr/Adr 002 Bm25 First Retrieval

ADR-002 — BM25-first retrieval before vector/graph search

Status: Accepted
Date: 2026-09-13

Context

Security queries often contain exact identifiers, product names, control IDs, and technical phrases where deterministic lexical matching is valuable.

Decision

Use BM25 with explicit field weights, exact-match bonuses, phrase bonuses, and a minimum relevance threshold as the first production retrieval method. Add vector and graph retrieval later behind measured regression benchmarks.

Consequences

Current retrieval is transparent, deterministic, fast, and easy to test. Semantic recall remains limited until hybrid retrieval is introduced.

Alternatives considered

Embedding-first retrieval and graph-only retrieval were deferred because they add complexity and weaker explainability before a quality baseline exists.