The RAG Basics: From Documents to Cited Answers

Whiteboard: RAG — The RAG Basics.

RAG is not simply pasting a few passages into a prompt. It is a knowledge pipeline whose quality depends on parsing, chunking, recall, prompting, and answer validation.

Core mental model

The offline path is Load → Clean → Chunk → Embed → Index; the online path is Query → Retrieve → Rerank/Filter → Generate → Cite. Version the boundary between them.

Key mechanics

Store source, page, section, and a content hash with every chunk. Pass only context above a relevance threshold and require traceable citations.

Python example

from dataclasses import dataclass

@dataclass
class Chunk:
    text: str
    source: str
    page: int
    chunk_id: str

def make_context(chunks: list[Chunk]) -> str:
    return "\n\n".join(f"[{c.chunk_id}] {c.text} (source={c.source}, page={c.page})" for c in chunks)

Course focus

This article turns the whiteboard into explicit engineering boundaries: define inputs and outputs first, then decide how state, failures, and observability work. The examples use Python and focus on durable design principles rather than a particular provider version; verify APIs against the documentation for your installed dependencies.

Engineering practice

Keep business rules in the application layer instead of hiding them in untestable prompts or route handlers.
Add timeouts, bounded retries, and idempotency keys to external calls; retries are not a complete error strategy.
Record a request id, latency, input version, model/index version, and outcome without logging sensitive raw content.
Use a small fixed regression set first, then monitor quality and cost with sampled production traffic.

Common mistakes

Drawing only the happy path and omitting timeouts, empty results, rate limits, and rollback paths.
Letting one function parse input, call providers, build prompts, and persist data.
Replacing typed contracts with string conventions that can only be verified by manual integration.

Production checklist

Inputs, outputs, and error responses have explicit schemas
External dependencies have timeouts, bounded retries, rate limits, and fallbacks
Logs, metrics, and traces can be correlated to one request
Critical paths have unit tests, integration tests, and offline evaluation samples
Secrets, user content, and provider responses follow least-privilege and privacy rules

Practice

Implement the smallest loop shown on the whiteboard. Inject a timeout, an empty result, and a malformed payload, then check whether the system remains stable and diagnosable. Add one metric that proves your optimization improved quality or latency.

Hands-on exercise

Create 30 questions with reference answers and sources. Measure retrieval hit rate, citation correctness, and abstention accuracy—not just whether the answer sounds plausible.