# 🔑 domainTokenizer

**Building small models that understand domain tokens — not just words.**

---

## The Idea

LLMs process text by breaking it into **tokens** (subword units like `ing`, `the`, `un-`). This tokenization is what enables Transformers to model sequential patterns.

But words are just one type of sequential data. Businesses generate massive amounts of **non-textual sequential data** every day — purchase transactions, banking flows, medical events, logistics chains, ad funnels. These carry rich structure that text tokenizers cannot capture.

**domainTokenizer** explores a different approach: what if we built tokenizers that encode **domain-specific entities** — products, transactions, medical codes, user actions — as first-class tokens, and then trained small, efficient models that understand domain patterns the way LLMs understand language?

```
Text LLM:      "The cat sat on the mat" → [The] [cat] [sat] [on] [the] [mat] → Transformer → next word

domainTokenizer: Customer purchase history → [HighEndElectronics] [WeekdayCredit] [Accessory+SameDay] → Transformer → next purchase
```

## Why This Matters

| Problem | Text Tokenizer | Domain Tokenizer |
|---------|---------------|-----------------|
| Product `SKU-8847291` | Split into meaningless fragments: `SK`, `U-`, `884`... | Encoded as Semantic ID: `[Electronics, 23, 7, 41]` with hierarchical meaning |
| Price `$79.99` | Fragmented: `$`, `79`, `.`, `99` | Tokenized as `price_bin_37` (73rd percentile = "mid-range") |
| Timestamp `2025-03-15` | Calendar-unaware text fragments | `[Wednesday, Afternoon, 2_days_later]` |
| Cross-field patterns | Lost in flat token stream | Discovered via BPE-like merging: `{Electronics + $50-100}` → composite token |

## Research Foundation

This project is grounded in 30+ papers from Google, Google DeepMind, and the broader research community. The key finding: **any sequential domain data can be tokenized and modeled with the LLM paradigm** — the challenge is *how* to tokenize.

Five paradigms have emerged:

| Paradigm | Method | Key Paper |
|----------|--------|-----------|
| **Semantic IDs** | RQ-VAE quantization of item embeddings | [TIGER](https://arxiv.org/abs/2305.05065) (Google, 2023) |
| **Action Tokenization** | BPE-like merging of feature patterns | [ActionPiece](https://arxiv.org/abs/2502.13581) (DeepMind, 2025) |
| **Transaction Tokenization** | Composite (date + amount + text) encoding | [Banking TF](https://arxiv.org/abs/2410.08243) (2024) |
| **Tabular Tokenization** | Relative magnitude encoding for numbers | [TP-BERTa](https://arxiv.org/abs/2403.01841) (2024) |
| **Universal Tokenization** | All modalities → shared discrete space | [Meta-Transformer](https://arxiv.org/abs/2307.10802) (2023) |

📄 **Full research report:** [`docs/research_report.md`](docs/research_report.md)

## Project Vision

### Phase 1: Research & Survey (✅ Current)
- Literature survey of domain tokenization methods
- Analysis of tokenization strategies across recommendation, finance, tabular, and universal domains
- Blueprint for a general-purpose domain tokenizer

### Phase 2: Core Tokenizer Library
- Implement per-field tokenizers:
  - `SemanticIDTokenizer` — RQ-VAE for entity encoding
  - `MagnitudeTokenizer` — relative magnitude binning for numerical values
  - `TemporalTokenizer` — calendar + relative delta encoding
  - `CompositeTokenizer` — BPE-like merging of multi-field patterns (ActionPiece-style)
- Schema-driven automatic tokenizer selection

### Phase 3: Pre-training Framework
- Self-supervised objectives: Masked Event Prediction, Next Event Prediction
- Small Transformer backbone (10M–350M parameters)
- Domain-agnostic training loop that works with any tokenizer configuration

### Phase 4: Domain Demos
- E-commerce: next purchase prediction, customer segmentation
- Finance: fraud detection, credit scoring
- Healthcare: clinical event prediction

## Repo Structure

```
domainTokenizer/
├── docs/
│   └── research_report.md    # Detailed research findings (30+ papers)
├── src/                       # (coming) Core library
│   ├── tokenizers/            # Per-field tokenizer implementations
│   ├── models/                # Small Transformer backbones
│   └── training/              # Pre-training and fine-tuning
├── examples/                  # (coming) Domain-specific demos
└── README.md
```

## Key References

| Paper | Year | What It Does | Link |
|-------|------|-------------|------|
| TIGER | 2023 | Semantic IDs for products via RQ-VAE | [arXiv](https://arxiv.org/abs/2305.05065) |
| ActionPiece | 2025 | BPE for user action sequences | [arXiv](https://arxiv.org/abs/2502.13581) |
| Banking TF | 2024 | Tokenizer for financial transactions | [arXiv](https://arxiv.org/abs/2410.08243) |
| LETTER | 2024 | Learnable item tokenization | [arXiv](https://arxiv.org/abs/2405.07314) |
| TP-BERTa | 2024 | Numerical value tokenization | [arXiv](https://arxiv.org/abs/2403.01841) |
| Meta-Transformer | 2023 | 12 modalities, one token space | [arXiv](https://arxiv.org/abs/2307.10802) |
| NTP Survey | 2024 | Comprehensive multimodal NTP taxonomy | [arXiv](https://arxiv.org/abs/2412.18619) |
| Nested Learning (HOPE) | 2025 | Continual learning via multi-timescale memory | [arXiv](https://arxiv.org/abs/2512.24695) |

See the [full reference table](docs/research_report.md#10-complete-paper-reference-table) with 31 papers in the research report.

## License

MIT

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*domainTokenizer is an early-stage research project exploring the frontier of domain-specific tokenization for small, efficient AI models.*