The Recursive Splitter That Respects Your Sentences
Chunking strategy is the silent killer of RAG accuracy. A splitter that ignores sentence boundaries produces fragments that retrieve poorly, while the recursive approach shown here keeps semantic units intact, directly improving the quality of answers a vector database can return.
Building a RAG pipeline starts with turning messy, heterogeneous data into clean, structured Document objects. LangChain's Loader ecosystem handles this with over 180 community adapters, but the real craft lies in what happens next: chunking. A naive character-count splitter destroys semantic coherence, but the RecursiveCharacterTextSplitter probes text with a hierarchy of separators — periods, question marks, then newlines — to find the most natural breakpoints. When a chunk still exceeds the target size, it recursively falls back to the next separator in the list, ensuring every piece is as close to the size limit as possible while keeping sentences whole.
A CheerioWebBaseLoader demonstrates the loading phase, using CSS selectors to extract only article body text from a raw HTML page, sidestepping the noise of navigation and sidebars. The splitter then takes over, configured with Chinese sentence-ending punctuation as the highest-priority separators and a 25% overlap between chunks. That overlap is the safety net: when a long sentence is inevitably broken, the duplicated text across chunk boundaries preserves the logical thread for retrieval.
The entire preprocessing chain — URL to HTTP response, DOM parsing, text extraction, recursive splitting — is a pipeline where every parameter is a trade-off. Chunk size, separator order, and overlap ratio directly control the recall-precision balance of the eventual vector search, making these seemingly mundane settings a core architectural decision.
The real engineering in RAG preprocessing is not the loading step but the chunking strategy, where language-specific separator hierarchies determine whether retrieved fragments carry coherent meaning or broken half-thoughts.
Cheerio's CSS-selector approach to web scraping is more resilient than regex-based HTML parsing because it mirrors how the page's own styles target content, making extraction logic stable even when surrounding markup changes.
The article's choice to set only three Chinese punctuation marks as explicit separators relies on the splitter's internal fallback chain, a design that keeps configuration minimal but assumes the developer knows the default English-oriented fallback exists and will activate.