embedding 0.1.3

# SPEC - Embedding Trainer Specification

## 1. Overview

### 1.1. Purpose
This document specifies the requirements, architecture, and implementation details for the Rust Embedding Trainer library and CLI tool. The project provides a comprehensive solution for training word embeddings from scratch using Skip-gram and CBOW algorithms.

### 1.2. Scope
- **Core library**: Implementation of embedding training algorithms
- **CLI interface**: Command-line interface for training and inference
- **Data processing**: Text preprocessing and vocabulary management
- **Model persistence**: Save/load models and embeddings
- **Performance**: Efficient training and inference capabilities
- **Extensibility**: Plugin system for custom algorithms

### 1.3. Definitions
- **Embedding**: Dense vector representation of words in continuous space
- **Skip-gram**: Neural network architecture that predicts context words from target words
- **CBOW**: Continuous Bag of Words architecture that predicts target words from context
- **Vocabulary**: Mapping of words to unique integer identifiers
- **Context window**: Number of surrounding words used for training

## 2. Requirements

### 2.1. Functional Requirements

#### 2.1.1. Training Algorithms
- **FR-001**: Skip-gram algorithm implementation
  - Support configurable context window size
  - Negative sampling capability
  - Efficient gradient calculation
  - Configurable embedding dimensions

- **FR-002**: CBOW (Continuous Bag of Words) algorithm
  - Support configurable context window size
  - Efficient gradient calculation
  - Configurable embedding dimensions
  - Batch processing support

#### 2.1.2. Data Processing
- **FR-004**: Text preprocessing
  - Lowercase conversion
  - Punctuation removal
  - Tokenization by whitespace
  - Empty sentence filtering

- **FR-005**: Vocabulary management
  - Build vocabulary from text data
  - Word-to-index mapping
  - Vocabulary size limits
  - Out-of-vocabulary handling

- **FR-006**: Data loading
  - File-based text input
  - Multiple format support (text, JSON)
  - Streaming support for large datasets

#### 2.1.3. Model Management
- **FR-007**: Model training
  - Configurable training parameters
  - Epoch-based training
  - Learning rate scheduling
  - Progress monitoring

- **FR-008**: Model persistence
  - Save/load complete models
  - Embedding export to multiple formats
  - Metadata storage (training parameters, vocabulary)
  - Compression support for large models

- **FR-009**: Similarity computation
  - Cosine similarity calculation
  - Efficient vector operations
  - Batch similarity queries
  - Similarity ranking

#### 2.1.4. CLI Interface
- **FR-010**: Training command
  - Input file specification
  - Output configuration
  - Training parameter tuning
  - Model type selection

- **FR-011**: Similarity command
  - Word pair similarity
  - Batch similarity queries
  - Similarity ranking output
  - Configuration file support

- **FR-012**: Model inspection
  - Model metadata display
  - Vocabulary inspection
  - Embedding statistics
  - Training history

- **FR-013**: Export functionality
  - Multiple export formats (text, JSON, binary)
  - Embedding format options
  - Vocabulary export
  - Model metadata export

#### 2.1.5. Evaluation & Validation
- **FR-014**: Validation framework
  - Train/validation split with configurable ratio
  - Automatic validation data generation from sentences
  - Validation metrics: accuracy, precision, recall, F1 score
  - Mean similarity and embedding quality score
  - Optional JSON metrics export

- **FR-015**: Evaluation metrics
  - Word pair similarity evaluation with threshold-based classification
  - Positive pair (consecutive words) vs negative pair (non-consecutive) discrimination
  - Embedding quality scoring based on norm and variance
  - Cosine similarity computation for all evaluation tasks

- **FR-016**: Validation CLI
  - `validate` command for evaluating saved models on held-out text
  - Vocabulary merge for out-of-vocabulary words in validation data
  - Metrics output to console and optional JSON file

### 2.2. Non-Functional Requirements

#### 2.2.1. Performance
- **NF-001**: Training efficiency
  - Optimize for large datasets
  - Parallel processing support
  - Memory-efficient operations
  - GPU acceleration (future)

- **NF-002**: Memory usage
  - Memory-mapped file support
  - Streaming processing
  - Efficient data structures
  - Garbage collection optimization

- **NF-003**: Speed requirements
  - Real-time similarity queries (< 10ms)
  - Efficient batch processing
  - Fast model loading (< 1s for 1M vocab)

#### 2.2.2. Reliability
- **NF-004**: Error handling
  - Comprehensive error types
  - Graceful failure modes
  - Recovery mechanisms
  - Detailed error messages

- **NF-005**: Data integrity
  - Input validation
  - Consistent model format
  - Checksum verification
  - Atomic file operations

#### 2.2.3. Usability
- **NF-006**: CLI usability
  - Intuitive command structure
  - Comprehensive help system
  - Progress indicators
  - Clear error messages

- **NF-007**: API usability
  - Clear documentation
  - Type-safe API
  - Comprehensive examples
  - Consistent naming conventions

#### 2.2.4. Maintainability
- **NF-008**: Code quality
  - Comprehensive test coverage (> 90%)
  - Clean architecture separation
  - Documentation requirements
  - Code review process

- **NF-009**: Documentation
  - API documentation
  - User guides
  - Development documentation
  - Performance benchmarks

### 2.3. Constraints

#### 2.3.1. Technical Constraints
- **TC-001**: Must use Rust programming language
- **TC-002**: Must use ndarray for numerical computations
- **TC-003**: Must support Windows, macOS, and Linux
- **TC-004**: Must be compatible with Rust 1.70+
- **TC-005**: Must use standard file formats for data exchange

#### 2.3.2. Business Constraints
- **BC-001**: Open source license (Apache-2.0)
- **BC-002**: No external API dependencies
- **BC-003**: Must work offline
- **BC-004**: Must be self-contained single binary

## 3. Architecture

### 3.1. System Architecture

```
┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
│   CLI Layer     │    │  Library Layer  │    │  Data Layer     │
│                 │    │                 │    │                 │
│┌─────────────┐  │    │┌─────────────┐  │    │┌─────────────┐  │
││   Parser    │  │    ││   Config    │  │    ││   Text Data │  │
│├─────────────┤  │    │├─────────────┤  │    │├─────────────┤  │
││ Commands    │  │    ││ Training    │  │    ││ Vocabulary   │  │
│├─────────────┤  │    ││ Algorithms  │  │    ││ Processing   │  │
││ Interface   │  │    │├─────────────┤  │    │├─────────────┤  │
│└─────────────┘  │    ││ Embedding  │  │    ││ I/O         │  │
│                 │    ││ Model       │  │    │└─────────────┘  │
│┌─────────────┐  │    │└─────────────┘  │    │                 │
││  CLI Logic  │  │    │┌─────────────┐  │    │┌─────────────┐  │
│├─────────────┤  │    ││ Serialization│  │    ││ Persistence  │  │
││ Error       │  │    ││├─────────────┤  │    ││├─────────────┤  │
││ Handling    │  │    │││  JSON/Bin  │  │    │││   Models    │  │
│└─────────────┘  │    │││  Formats   │  │    ││├─────────────┤  │
└─────────────────┘    ││└─────────────┘  │    │││   Embeddings│  │
                       ││┌─────────────┐  │    ││└─────────────┘  │
                       │││ Utilities   │  │    │└─────────────┘  │
                       ││├─────────────┤  │    │                 │
                       │││ Text Process│  │    └─────────────────┘
                       │││ Similarity  │  │
                       │││ Helpers     │  │
                       ││└─────────────┘  │
                       └─────────────────┘
```

### 3.2. Component Architecture

#### 3.2.1. Core Library Components

**TrainingConfig**
```rust
pub struct TrainingConfig {
    pub embedding_dim: usize,          // Output embedding dimension
    pub learning_rate: f64,           // Learning rate for training
    pub epochs: usize,                 // Number of training epochs
    pub batch_size: usize,             // Mini-batch size
    pub context_window: usize,        // Context window size
    pub negative_samples: usize,      // Number of negative samples
    pub model_type: ModelType,        // Algorithm to use
    pub lr_schedule: LearningRateSchedule, // Learning rate schedule
    pub early_stopping: Option<EarlyStoppingConfig>, // Early stopping config
    pub l2_regularization: Option<f64>, // L2 regularization coefficient
    pub gradient_clip: Option<f32>,   // Maximum gradient norm
    pub validation_ratio: Option<f64>, // Fraction of data for validation
}
```

**TrainingData**
```rust
pub struct TrainingData {
    pub sentences: Vec<Vec<String>>,   // Tokenized sentences
    pub vocab: HashMap<String, usize>, // Word to index mapping
    pub reverse_vocab: Vec<String>,  // Index to word mapping
}
```

**EmbeddingModel**
```rust
pub struct EmbeddingModel {
    pub embeddings: Array2<f32>,      // Word embedding matrix
    pub config: TrainingConfig,       // Training configuration
    pub vocab_size: usize,            // Vocabulary size
}
```

#### 3.2.2. CLI Components

**Command Parser**
```rust
#[derive(Subcommand)]
enum Commands {
    Train { /* Training parameters */ },
    Similarity { /* Similarity query */ },
    Info { /* Model inspection */ },
    Export { /* Export functionality */ },
    Validate { /* Validation on held-out data */ },
    Interactive { /* Interactive query mode */ },
}
```

#### 3.2.3. Data Processing Components

**Text Processor**
- Tokenization: Split text into words
- Normalization: Lowercase, punctuation removal
- Vocabulary building: Create word-to-index mappings

**Embedding Trainer**
- Skip-gram implementation
- CBOW implementation

### 3.3. Data Flow

#### 3.3.1. Training Flow
```
Input Text → Text Processing → Vocabulary Building → Model Initialization → Training → Model Output
    ↓               ↓                  ↓                   ↓               ↓              ↓
Raw text → Cleaned text → Word mappings → Random embeddings → Gradient updates → Trained model
```

#### 3.3.2. Validation Flow
```
Trained Model + Validation Text → Text Processing → Vocabulary Merge →
    Validation Pair Generation → Similarity Evaluation → Metrics Output
```

#### 3.3.3. Inference Flow
```
Query Words → Vocabulary lookup → Embedding retrieval → Similarity calculation → Results
    ↓              ↓                   ↓                  ↓                ↓
Text input → Index mapping → Vector extraction → Mathematical computation → Output
```

## 4. Implementation Details

### 4.1. Algorithm Details

#### 4.1.1. Skip-gram Algorithm
**Objective**: Maximize log probability of context words given target word

**Mathematical Formulation**:
```
maximize Σ_{t=1 to T} Σ_{-m≤j≤m, j≠0} log P(w_{t+j} | w_t; θ)
```

**Gradient Calculation**:
```
∂J/∂θ = -Σ_{t,j} [y - P(w_{t+j} | w_t)] ∂P/∂θ
```

**Implementation Notes**:
- Hierarchical softmax or negative sampling for efficiency
- Gradient descent with configurable learning rate
- Context window parameter for training

#### 4.1.2. CBOW Algorithm
**Objective**: Maximize log probability of target word given context words

**Mathematical Formulation**:
```
maximize Σ_{t=1 to T} log P(w_t | w_{t-m}, ..., w_{t+m}; θ)
```

**Gradient Calculation**:
```
∂J/∂θ = -Σ_{t} [y - P(w_t | context)] ∂P/∂θ
```

**Implementation Notes**:
- Average context word embeddings
- Similar gradient structure to Skip-gram
- Context window parameter for training

### 4.2. Performance Considerations

#### 4.2.1. Memory Optimization
- Use ndarray for efficient array operations
- Implement lazy loading for large datasets
- Streaming sentence iterators for large datasets
- Batch processing to reduce memory overhead

#### 4.2.2. Computational Efficiency
- Iterator-based batch processing
- Vectorized operations using ndarray
- Efficient similarity calculations
- Cache-friendly data access patterns

#### 4.2.3. Algorithm Optimizations
- Negative sampling for Skip-gram
- Hierarchical softmax alternatives
- Learning rate scheduling
- Early stopping mechanisms

### 4.3. Error Handling

#### 4.3.1. Error Types
```rust
pub enum TrainingError {
    InvalidInput(String),
    VocabularyError(String),
    ModelError(String),
    IOError(String),
    ConfigurationError(String),
}
```

#### 4.3.2. Error Recovery
- Graceful handling of missing words
- Fallback mechanisms for corrupted data
- Transactional file operations
- Consistent state management

## 5. Testing Strategy

### 5.1. Unit Testing
- **Algorithm testing**: Verify mathematical correctness
- **Data processing**: Test tokenization and vocabulary building
- **Model operations**: Test embedding operations and similarity
- **Serialization**: Test save/load functionality

### 5.2. Integration Testing
- **End-to-end training**: Complete training workflow
- **CLI functionality**: Test all command interfaces
- **File I/O**: Test loading and saving different formats
- **Error scenarios**: Test edge cases and error handling

### 5.3. Performance Testing
- **Training benchmarks**: Speed and memory usage
- **Query performance**: Similarity calculation speed
- **Large dataset handling**: Scalability testing
- **Memory usage patterns**: Peak memory consumption

### 5.4. Test Data
- **Small datasets**: For unit testing
- **Medium datasets**: For integration testing
- **Large datasets**: For performance testing
- **Real-world data**: For validation testing

## 6. Deployment

### 6.1. Build Requirements
- Rust toolchain 1.70+
- Cargo build system
- Standard C compiler for native dependencies
- Cross-platform compilation support

### 6.2. Distribution
- Binary distribution via crates.io
- Source code on GitHub
- Docker container for easy deployment
- Platform-specific packages for Linux, macOS, Windows

### 6.3. Documentation
- API documentation with rustdoc
- User guides and tutorials
- Performance benchmarks
- Contributing guidelines

## 7. Security Considerations

### 7.1. Input Validation
- File path validation
- Memory safety guarantees
- Buffer overflow protection
- Integer overflow handling

### 7.2. Data Protection
- Secure file handling
- Memory wiping for sensitive data
- Access control mechanisms
- Audit logging capabilities

### 7.3. Supply Chain Security
- Dependency vulnerability scanning
- Secure build process
- Code review requirements
- Integrity verification

## 8. Version Control

### 8.1. Version Numbering
- **Major**: Breaking changes
- **Minor**: New features, backward compatible
- **Patch**: Bug fixes, backward compatible

### 8.2. Change Management
- Semantic versioning compliance
- Detailed changelog maintenance
- Beta release process
- Deprecation policy

## 9. Maintenance

### 9.1. Code Quality
- Static code analysis
- Automated testing
- Code review process
- Refactoring guidelines

### 9.2. Performance Monitoring
- Benchmark tracking
- Memory usage monitoring
- CPU profiling
- Load testing

### 9.3. Community Support
- Issue tracking system
- Documentation updates
- User feedback integration
- Performance optimization

---

**Specification Version**: 1.1  
**Last Updated**: 2026-06-10  
**Review Date**: Quarterly  
**Approvals**: Technical Lead, Project Manager