Update MIGRATION.md for external ud-hf-parquet-tools library

Major updates to reflect architectural changes:

**New Section: Helper Functions Moved to External Library**
- Documents that parse_feats, parse_misc, write_conllu, etc. are no longer
part of the dataset
- Provides installation instructions for ud-hf-parquet-tools package
- Shows updated import examples using the external library
- Includes alternative for users who don't need helper functions (work with
raw strings directly)

**Updated "What's New" Section**
- Added overview of architecture changes (Parquet, no Python script, external
helper library)
- Clarified data changes (MWT bug fix, new MWT field, enhanced metadata)

**New Issue: Helper Function Import Errors**
- Added Issue 4 documenting ImportError when trying to import from
non-existent universal_dependencies module
- Provides clear solution with installation and import examples

**Enhanced Summary**
- Added "v2.0 is modular" to key takeaways
- Updated migration checklist with helper library installation steps
- Separated estimated migration time for basic vs. helper function users
- Added resources section with links to dataset, helper library, and changelog

**Updated Support Section**
- Added link to ud-hf-parquet-tools documentation

All code examples now use correct imports from ud-hf-parquet-tools package.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

MIGRATION.md

@@ -2,6 +2,18 @@
 
 This guide helps you migrate from Universal Dependencies dataset loader v1.x to v2.0.
 
+## What's New in v2.0
+
+**Architecture Changes:**
+- **Parquet format**: Native support with datasets >=4.0.0 (5-10x faster loading)
+- **No Python script**: Dataset no longer requires `trust_remote_code=True`
+- **External helper library**: CoNLL-U processing utilities moved to [`ud-hf-parquet-tools`](https://github.com/bot-zen/ud-hf-parquet-tools)
+
+**Data Changes:**
+- **MWT bug fix**: Token sequences now correctly exclude Multi-Word Token surface forms
+- **MWT field added**: New structured `mwt` field with Multi-Word Token information
+- **Enhanced metadata**: Includes `num_fused` (MWT counts) in statistics
+
 ## Quick Start
 
 ### For Users with datasets >=4.0.0
@@ -186,6 +198,73 @@ dataset = load_dataset(
 )
 ```
 
+## Helper Functions Moved to External Library
+
+**Important:** Helper functions for CoNLL-U processing are now in a separate package.
+
+### What Moved
+
+The following functions are **no longer part of the dataset**:
+- `parse_feats()`, `parse_misc()`, `parse_deps()` - Parse CoNLL-U field strings
+- `write_conllu()`, `example_to_conllu()` - Export data to CoNLL-U format
+- Various internal conversion utilities
+
+### How to Access Helper Functions
+
+If you need CoNLL-U processing utilities, install the external library:
+
+```bash
+pip install ud-hf-parquet-tools
+```
+
+Then import from the package:
+
+```python
+from datasets import load_dataset
+from ud_hf_parquet_tools import parse_feats, parse_misc, write_conllu
+
+# Load dataset
+ds = load_dataset("commul/universal_dependencies", "en_ewt", split="train")
+
+# Parse optional fields
+sentence = ds[0]
+for i, token in enumerate(sentence['tokens']):
+    feats = parse_feats(sentence['feats'][i])  # Returns dict or {}
+    misc = parse_misc(sentence['misc'][i])      # Returns dict or {}
+    print(f"{token}: UPOS={sentence['upos'][i]}, feats={feats}, misc={misc}")
+
+# Export back to CoNLL-U format
+write_conllu(ds, "output.conllu")
+```
+
+**Library Documentation:** https://github.com/bot-zen/ud-hf-parquet-tools
+
+### If You Don't Need Helper Functions
+
+Most users only need the dataset itself and can work directly with the fields:
+
+```python
+from datasets import load_dataset
+
+ds = load_dataset("commul/universal_dependencies", "en_ewt", split="train")
+
+# Access data directly
+sentence = ds[0]
+print(f"Tokens: {sentence['tokens']}")
+print(f"POS tags: {sentence['upos']}")
+print(f"Dependencies: {sentence['deprel']}")
+
+# FEATS and MISC are strings in CoNLL-U format
+print(f"Features (raw): {sentence['feats'][0]}")  # e.g., "Case=Nom|Number=Sing"
+print(f"Misc (raw): {sentence['misc'][0]}")       # e.g., "SpaceAfter=No"
+
+# Parse manually if needed (simple cases)
+feats_str = sentence['feats'][0]
+if feats_str:
+    feats_dict = dict(kv.split('=') for kv in feats_str.split('|'))
+    print(f"Features (parsed): {feats_dict}")
+```
+
 ## New Features in v2.0
 
 ### 1. Parquet Format (5-10x Faster Loading)
@@ -344,13 +423,35 @@ tokens = example["tokens"]
 mwts = example.get("mwt", [])  # Empty list if not present
 ```
 
+### Issue 4: Helper Function Import Errors
+
+**Error:**
+```python
+from universal_dependencies import parse_feats
+# ImportError: No module named 'universal_dependencies'
+```
+
+**Cause:** Helper functions moved to separate library
+
+**Solution:**
+```bash
+# Install the helper library
+pip install ud-hf-parquet-tools
+
+# Update imports
+from ud_hf_parquet_tools import parse_feats, parse_misc, write_conllu
+```
+
+Or work with raw strings directly (see "If You Don't Need Helper Functions" section above).
+
 ## Support
 
 If you encounter issues during migration:
 
 1. Check the [CHANGELOG.md](CHANGELOG.md) for detailed changes
 2. Review the [README.md](README.md) for updated examples
-3. Report issues at: https://github.com/UniversalDependencies/UD_HuggingFace/issues
+3. Helper library documentation: https://github.com/bot-zen/ud-hf-parquet-tools
+4. Report issues at: https://huggingface.co/datasets/commul/universal_dependencies/discussions
 
 ## Summary
 
@@ -360,13 +461,23 @@ If you encounter issues during migration:
 ✅ **v2.0 is faster:** Parquet format is 5-10x quicker
 ✅ **v2.0 is more secure:** No remote code execution
 ✅ **v2.0 adds features:** MWT information now available
+✅ **v2.0 is modular:** Helper functions available as separate library
 
 **Migration Checklist:**
 
 - [ ] Upgrade to datasets >=4.0.0
 - [ ] Test your code with v2.0 data
 - [ ] Update token count expectations (if using MWT treebanks)
-- [ ] Utilize new MWT field for research (optional)
 - [ ] Update any hard-coded token indices (if applicable)
+- [ ] If using helper functions: Install `ud-hf-parquet-tools` and update imports
+- [ ] If exporting to CoNLL-U: Use `write_conllu()` from `ud-hf-parquet-tools`
+- [ ] Utilize new MWT field for research (optional)
+
+**Estimated Migration Time:**
+- Basic usage: 15-30 minutes
+- With helper functions: +10 minutes (install library, update imports)
 
-**Estimated Migration Time:** 15-30 minutes for most users
+**Resources:**
+- Dataset repository: https://huggingface.co/datasets/commul/universal_dependencies
+- Helper library: https://github.com/bot-zen/ud-hf-parquet-tools
+- CHANGELOG: [CHANGELOG.md](CHANGELOG.md)