KnowledgeBase/docs/design/feat-query-expansion-hyde.md

Feature Design: Query Expansion & HyDE Integration

This document outlines the design for improving search relevance in Lumina using Query Expansion (Multi-Query) and Hypothetical Document Embeddings (HyDE).

Problem Statement

The current search implementation relies on the user's original query. Simple vector search can sometimes fail to match relevant documents due to:

1. Keyword Mismatch: The user might use different terminology than the document.
2. Semantic Gap: The query might be too brief to capture the full semantic context required for a good vector match.

Proposed Solution

1. Query Expansion (Multi-Query)

We will use an LLM to generate 3 unique variations of the user's query. This helps to:

• Capture different facets of the user's intent.
• Increase the probability of hitting relevant segments in the knowledge base.

2. HyDE (Hypothetical Document Embeddings)

We will use an LLM to generate a brief "hypothetical" answer to the user's query.

• Instead of embedding the question, we embed the hypothetical answer.
• This often results in better vector matches because we are comparing "answer-like" vectors with "document-like" segments.

Technical Implementation

Backend Changes

RagService (server/src/rag/rag.service.ts)

• New Methods:
  • expandQuery(query: string, userId: string): Promise<string[]>: Generates 3 variations of the query.
  • generateHyDE(query: string, userId: string): Promise<string>: Generates a hypothetical document.
• Update searchKnowledge:
  • Add enableQueryExpansion and enableHyDE parameters.
  • Implement logic to handle multiple search requests (concurrently) and deduplicate results.

ChatService (server/src/chat/chat.service.ts)

• Pass the new search options from user settings or request parameters.

Frontend Changes

types.ts (web/types.ts)

• Update AppSettings to include enableQueryExpansion and enableHyDE.

SettingsDrawer.tsx

• Add UI toggles for these new search enhancement features.

Verification Plan

Backend Logs

• Verify that LLM calls for expansion and HyDE are being made.
• Log the generated queries and hypothetical documents for debugging.

Manual Verification

• Compare search results with and without these features enabled for complex queries.