# Research: Neurosurgeon RAG Learning Platform

**Branch**: `001-neuro-rag-learning`
**Date**: 2026-03-31

---

## 1. Spring Boot 4 + Spring AI Versions & BOM

**Decision**: Spring Boot **4.0.5** + Spring AI **1.1.4**.

**Rationale**: Spring Boot 4.0.5 is GA (released February 2026) — this matches the user's
original requirement. Spring AI 1.1.4 is the current stable release compatible with
Spring Boot 4.x. Spring AI 2.0.0-M4 is available in preview but not used (KISS — no
preview dependencies).

**Maven BOM** (in `<dependencyManagement>`):
```xml
<dependency>
  <groupId>org.springframework.ai</groupId>
  <artifactId>spring-ai-bom</artifactId>
  <version>1.1.4</version>
  <type>pom</type>
  <scope>import</scope>
</dependency>
```

**Key starters** (versions managed by BOM):
```xml
<!-- pgvector vector store -->
<dependency>
  <groupId>org.springframework.ai</groupId>
  <artifactId>spring-ai-starter-vector-store-pgvector</artifactId>
</dependency>

<!-- OpenAI (embedding + chat; swap for any other provider) -->
<dependency>
  <groupId>org.springframework.ai</groupId>
  <artifactId>spring-ai-starter-openai</artifactId>
</dependency>

<!-- PDF document reader (Spring AI native, Apache PDFBox-based) -->
<dependency>
  <groupId>org.springframework.ai</groupId>
  <artifactId>spring-ai-pdf-document-reader</artifactId>
</dependency>

<!-- PostgreSQL JDBC driver -->
<dependency>
  <groupId>org.postgresql</groupId>
  <artifactId>postgresql</artifactId>
  <scope>runtime</scope>
</dependency>
```

**Alternatives considered**: Spring AI 2.0.0-M4 — rejected (milestone, KISS principle).

---

## 2. Spring AI RAG Pipeline

**Decision**: Use Spring AI's `PagePdfDocumentReader`, `EmbeddingModel`, `PgVectorStore`,
and `ChatClient` with `QuestionAnswerAdvisor` for RAG.

**Key classes**:

| Component | Class / Interface | Purpose |
|-----------|-------------------|---------|
| Document ingestion | `PagePdfDocumentReader` | Parse PDF pages to `Document` objects |
| Chunking | `TokenCountBatchingStrategy` | Split docs to respect token limits |
| Embedding | `EmbeddingModel` | Convert text chunks to vectors |
| Storage | `VectorStore` / `PgVectorStore` | Persist and search embeddings |
| RAG query | `QuestionAnswerAdvisor` | Augments prompt with retrieved context |
| Chat | `ChatClient` | Fluent API for LLM interactions |

**RAG pipeline flow**:
```
PDF file
  → PagePdfDocumentReader     (extract text per page as Document)
  → TokenCountBatchingStrategy (chunk to embedding token limit)
  → EmbeddingModel.embed()    (vectorise each chunk)
  → PgVectorStore.add()       (persist chunk + vector + metadata)

User query
  → ChatClient.prompt()
      .advisors(new QuestionAnswerAdvisor(vectorStore))
      .user(question)
      .call()
  → QuestionAnswerAdvisor runs similaritySearch, injects context
  → ChatModel generates response grounded in retrieved chunks
```

**application.properties**:
```properties
spring.ai.vectorstore.pgvector.dimensions=1536
spring.ai.vectorstore.pgvector.distance-type=COSINE_DISTANCE
spring.ai.vectorstore.pgvector.index-type=HNSW
spring.ai.vectorstore.pgvector.initialize-schema=true

spring.ai.openai.api-key=${OPENAI_API_KEY}
spring.ai.openai.chat.options.model=gpt-4o
spring.ai.openai.embedding.options.model=text-embedding-3-small
```

**Rationale**: `QuestionAnswerAdvisor` is the Spring AI-idiomatic RAG pattern — zero
boilerplate. `EmbeddingModel` and `ChatClient` are interfaces; swapping the LLM provider
is a single property change (Principle II).

---

## 3. PDF Ingestion & Chunking

**Decision**: `PagePdfDocumentReader` (from `spring-ai-pdf-document-reader`) for text
extraction; default `TokenCountBatchingStrategy` for chunking.

**Approach**:
```java
PagePdfDocumentReader reader = new PagePdfDocumentReader(
    new FileSystemResource("textbook.pdf"),
    PdfDocumentReaderConfig.builder()
        .withPagesPerDocument(1)   // one Document per page
        .build()
);
List<Document> pages = reader.get();
vectorStore.add(pages);  // batching + embedding handled internally
```

- Each `Document` carries metadata: source filename, page number.
- `TokenCountBatchingStrategy` ensures chunks fit the embedding model's context window
  (~8 000 tokens for OpenAI models).
- Custom metadata (`book_id`, `book_title`, `chunk_type`) is added before calling
  `vectorStore.add()`.

**Rationale**: `PagePdfDocumentReader` is the recommended Spring AI PDF reader for
text-focused RAG — lighter than the Tika reader and purpose-built for PDFs.

**Alternatives considered**: `TikaDocumentReader` — provides multi-format support but is
heavier; rejected for POC (only PDFs are in scope).

---

## 4. Diagram / Visual Content Handling

**Decision**: Extract diagram captions and surrounding text as text chunks tagged
`chunk_type=diagram`. No pixel-level image embedding for the POC.

**Approach**:
- `PagePdfDocumentReader` extracts all text including figure captions
  (e.g., `"Figure 3.2: Circle of Willis anatomy..."`).
- A post-processing step identifies lines matching caption patterns
  (`^(Figure|Fig\.|Table|Diagram)\s+[\d.]+`) and tags those `Document` objects with
  `metadata.put("chunk_type", "diagram")`.
- The caption text plus the surrounding descriptive paragraph are included in the chunk,
  making the diagram content semantically searchable.

**Rationale**: This is the simplest approach that satisfies FR-003 within KISS constraints.
The spec explicitly excludes pixel-level image search from the POC scope.

**Future upgrade path**: Use a vision model (GPT-4o vision) to generate text descriptions
of extracted images and add them as additional `chunk_type=diagram` documents — no
architectural change needed, just a new processing step.

---

## 5. Simple Shared-Password Authentication

**Decision**: Spring Security HTTP Basic with a single in-memory user.

**Spring Security config**:
```java
@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests(a -> a.anyRequest().authenticated())
            .httpBasic(Customizer.withDefaults())
            .csrf(AbstractHttpConfigurer::disable);  // REST API — no CSRF needed
        return http.build();
    }

    @Bean
    public UserDetailsService userDetailsService(
            @Value("${app.auth.password}") String password) {
        UserDetails user = User.builder()
            .username("neurosurgeon")
            .password("{noop}" + password)   // {noop} = plain text for POC
            .roles("USER")
            .build();
        return new InMemoryUserDetailsManager(user);
    }
}
```

```properties
# application.properties
app.auth.password=${APP_PASSWORD}
```

**Rationale**: Zero database dependency; zero token management. The Vue.js frontend
sets `Authorization: Basic <base64>` via Axios `auth` config. Fully sufficient for
< 10 trusted users on a private network (POC constraint).

**Alternatives considered**: JWT — rejected (requires token endpoint, more code);
custom API key filter — rejected (HTTP Basic is simpler and just as secure for this scale).

---

## 6. Vue.js 3 Project Structure

**Decision**: Vite + Vue 3 + TypeScript + Pinia + Vue Router + Axios.

**Standard layout** (`npm create vue@latest`):
```
frontend/src/
├── components/      # Reusable UI components (BookCard, ChatMessage, etc.)
├── views/           # Route-level pages: UploadView, TopicsView, ChatView
├── stores/          # Pinia: bookStore, topicStore, chatStore
├── services/        # api.ts — Axios instance with base URL + Basic auth header
├── router/          # index.ts — Vue Router routes
└── main.ts
```

**Axios setup** (`services/api.ts`):
```typescript
import axios from 'axios'

export const api = axios.create({
  baseURL: import.meta.env.VITE_API_URL ?? 'http://localhost:8080/api/v1',
  auth: {
    username: 'neurosurgeon',
    password: import.meta.env.VITE_APP_PASSWORD
  }
})
```

**Rationale**: Axios handles HTTP Basic auth via its `auth` config — no manual
`btoa()` needed. Pinia is Vue's official state manager (replaced Vuex).

---

## 7. pgvector Configuration & Schema

**Decision**: Spring AI auto-creates the `vector_store` table via `initialize-schema=true`.
Application tables use Flyway migrations.

**Required PostgreSQL extensions** (run once on the provided database):
```sql
CREATE EXTENSION IF NOT EXISTS vector;
CREATE EXTENSION IF NOT EXISTS hstore;
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
```

**Spring AI auto-created table**:
```sql
CREATE TABLE IF NOT EXISTS vector_store (
    id       uuid DEFAULT uuid_generate_v4() PRIMARY KEY,
    content  TEXT NOT NULL,
    metadata JSONB NOT NULL DEFAULT '{}',
    embedding VECTOR(1536) NOT NULL
);
CREATE INDEX ON vector_store USING HNSW (embedding vector_cosine_ops);
```

**Key properties**:

| Property | Value | Notes |
|----------|-------|-------|
| `dimensions` | `1536` | Matches `text-embedding-3-small`; update if provider changes |
| `distance-type` | `COSINE_DISTANCE` | Standard for normalised text embeddings |
| `index-type` | `HNSW` | O(log N) search; best default for POC |
| `initialize-schema` | `true` | Auto-create table on startup (safe for POC) |

**Embedding dimensions note**: if the LLM provider is switched (e.g., to Ollama with a
768-dim model), update `dimensions` in properties **and** re-embed all books — the
`vector_store` table must be recreated with the new dimension.

**Alternatives considered**: IVFFlat index — more memory-efficient but slower; NONE for very
small datasets. HNSW is the best default for a POC where correctness matters more than
storage.