medium★ EssentialCohere Microsoft Elastic

How do you combine lexical (BM25) and semantic (vector) retrieval, and what is Reciprocal Rank Fusion?

Pure vector search misses exact terms; pure keyword search misses meaning. The signal is knowing why each fails alone and how to merge two rankings on incomparable scales without hand-tuning weights. Here is the answer.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

Unlock the other 754 answers · ₹2,000 / $25includes both full courses · progress stays saved · 6 months · one payment · no auto-renew

LEARN THE BACKGROUND

These lessons teach the material this question tests, in order and from the beginning.

Applied AI Engineering·RetrievalFree14mWhy your search misses the obvious answerPure vector search fails in two specific, predictable ways, and both have standard fixes that most first systems are missing. This lesson covers the two-stage design that turns a demo into something that finds the right passage.

UP NEXT ON YOUR JOURNEY

Next in this trackHow do you handle multi-hop questions in RAG (questions needing several pieces of evidence)?Next in this trackHow do you keep a RAG system's knowledge fresh (index updates, stale data, changing documents)?Next in this trackWhat is late interaction (ColBERT), and how does it sit between bi-encoders and cross-encoders?

DISCUSSION · 0

No comments yet — be the first to share your approach.