SindhiLM-Tokenizer-v3

SindhiLM Tokenizer v3 (Unigram)

This tokenizer was specifically engineered and empirically tested for the Sindhi language, transitioning from a Byte-Level BPE model to a Unigram algorithm with Whitespace pre-tokenization to respect Sindhi morphological boundaries and prevent the shattering of Perso-Arabic text.

Corpus Cleaning

Trained on 200000 documents from a newly filtered version of the Sindhi corpus. Filtering was upgraded from a heuristic script-ratio check to a FastText LangID (lid.176) pass to aggressively remove Farsi, Urdu, and Pashto contamination.

Empirical Verification Results

• Vocabulary Size: 32000
• Algorithm: Unigram
• Average Fertility Rate: 1.619 tokens per word (Tested on fresh, held-out documents).
• Ground-Truth Morpheme Split Test: 1/9 exact matches against native-speaker evaluations.
• Digraph Integrity: The گھ (gh) aspirated digraph is SOMETIMES split by this tokenizer.
• Izafat Case (ءَ / ء): Words containing the Sindhi genitive construction previously shattered into 5-6 fragments in BPE. Under this Unigram model, they tokenize into 3 or fewer logical pieces (Passed verification).

Known Limitations

The following hand-corrected morpheme boundary splits failed during testing. This implies ambiguity requiring POS context unavailable to a pure subword tokenizer:

• گھرن: Expected ['گھر', 'ن'], but the tokenizer split into ['گ', 'ھ', 'ر', 'ن'].
• ڇوڪري: Expected ['ڇوڪر', 'ي'], but the tokenizer split into ['ڇوڪري'].
• استادن: Expected ['استاد', 'ان'], but the tokenizer split into ['استادن'].
• لکھندو: Expected ['لکھ', 'ندو'], but the tokenizer split into ['ل', 'ک', 'ھندو'].
• پڙهيل: Expected ['پڙھ', 'يل'], but the tokenizer split into ['پڙهيل'].
• وڃي: Expected ['وڃ', 'ي'], but the tokenizer split into ['وڃي'].
• ننڍڙو: Expected ['ننڍ', 'ڙو'], but the tokenizer split into ['ننڍڙو'].
• لکندڙ: Expected ['لکھ', 'ند', 'ڙ'], but the tokenizer split into ['لکندڙ'].