Skip to main content

Understanding Retrieval-Augmented Generation (RAG)

Before diving into implementation, let's understand what RAG is and why it's become such an important pattern in AI applications.

What is RAG?​

Retrieval-Augmented Generation (RAG) is an AI architecture pattern that enhances large language models (LLMs) by retrieving relevant information from external knowledge sources before generating responses.

The core workflow consists of:

  1. Retrieval: Finding relevant information from a knowledge base
  2. Augmentation: Incorporating that information into the context
  3. Generation: Using an LLM to generate a response based on the augmented context

How RAG Works

1

User Query

The user submits a question, such as 'How does MongoDB Atlas Vector Search work?'

Why Use RAG?​

RAG addresses several limitations of standalone LLMs:

  1. Up-to-date information: LLMs are trained on historical data and don't know about recent events
  2. Domain-specific knowledge: Standard LLMs lack deep expertise in specialized domains
  3. Hallucination reduction: By grounding responses in retrieved facts, RAG reduces fabricated answers
  4. Data privacy: Your proprietary data stays in your control rather than being sent to the LLM provider
  5. Cost efficiency: Retrieval can reduce the context length needed for complex questions

Core Components of RAG​

A typical RAG system has these key components:

1. Vector Database​

Stores document embeddings and enables semantic search. MongoDB Atlas Vector Search provides this functionality with advanced features like:

  • High-dimensional vector storage
  • Approximate nearest neighbor (ANN) search algorithms
  • Hybrid filtering (combining vector similarity with traditional queries)
  • Horizontal scaling for large collections

2. Document Processing Pipeline​

Transforms raw documents into searchable chunks and embeddings:

  • Document loading from various sources
  • Text chunking strategies
  • Embedding generation
  • Metadata extraction

3. Retrieval Mechanism​

Finds the most relevant information given a query:

  • Vector similarity search
  • Re-ranking for relevance
  • Metadata filtering
  • Results fusion (combining multiple retrieval methods)

4. Augmentation Strategy​

How retrieved content is added to the prompt:

  • Document concatenation
  • Structured formatting
  • Relevance scoring
  • Dynamic prompt construction

5. LLM Interface​

The generation component that produces the final output:

  • Prompt engineering
  • Response generation
  • Output formatting
  • Fallback handling

The RAG Architecture with MongoDB Atlas​

When building RAG with MongoDB Atlas, the architecture typically looks like this:

  1. MongoDB Atlas serves as the vector database
  2. Embedding models (like OpenAI's text-embedding-3-small) create vector representations
  3. mongodb-rag library handles document processing and retrieval
  4. LLM providers (OpenAI, Anthropic, etc.) generate the final responses

In the following sections, you'll implement each piece of this architecture to build a complete RAG system.

Vector Search Fundamentals​

Before moving on, it's important to understand some key concepts about vector search:

Embeddings​

Embeddings are numerical representations of text, images, or other data that capture semantic meaning. Similar concepts have similar vector representations, enabling "similarity search."

For example, these sentences would have similar embeddings:

  • "The dog chased the ball"
  • "A canine pursued a round toy"

Vector Similarity Metrics​

Different distance functions measure similarity between vectors:

  • Cosine similarity: Measures the angle between vectors (1.0 = identical direction)
  • Euclidean distance: Measures straight-line distance between points
  • Dot product: Simple multiplication of vector components

For large vector collections, exact search is inefficient. ANN algorithms like HNSW (Hierarchical Navigable Small Worlds) provide faster results with minimal accuracy trade-offs.

Let's Check Your Understanding​

RAG Concepts Check

Question 1: What are the three main stages in the RAG workflow?
Vectorization, Augmentation, Generation
Retrieval, Augmentation, Generation
Retrieval, Analysis, Generation
Research, Augmentation, Generation

Moving Forward​

Now that you understand the core concepts behind RAG, let's set up your MongoDB Atlas environment to support vector search capabilities.