Advanced RAG Architecture

A deep-dive walkthrough of production-grade Retrieval-Augmented Generation in .NET — covering document ingestion pipelines, PDF/Word/Excel/HTML parsing, OCR for scanned documents, semantic chunking and overlap strategies, parent-child retrieval, hierarchical indexing, query rewriting and expansion, hybrid search with Reciprocal Rank Fusion, cross-encoder reranking, metadata filtering, context compression, GraphRAG, agentic RAG, corrective RAG, RAG caching, and benchmarking — with C# code for every technique and guidance on when each one is worth its cost.

Table of Contents

Introduction

Document Ingestion Pipelines

Parsing PDF, Word, Excel, and HTML

OCR for Scanned Documents

Semantic Chunking

Chunk Overlap Strategies

Parent-Child Retrieval

Hierarchical Indexing

Query Rewriting

Query Expansion

Hybrid Search (Keyword + Vector)

Reciprocal Rank Fusion (RRF)

Cross-Encoder Reranking

Metadata Filtering

Context Compression

GraphRAG

Agentic RAG

Corrective RAG

RAG…