arXiv:2508.08424cs.CLcs.AI2025-08The 14th Internati…被引 7

对比发现:对复杂形态语言,无词边界分词优于传统分词法。

Rethinking Tokenization for Rich Morphology: The Dominance of Unigram over BPE and Morphological Alignment

  • 用无词边界分词算法处理泰卢固语,效果优于传统字节对编码。
  • 在泰卢固语上,无词边界分词模型准确率高出约5.2个百分点。
  • 融合形态信息预切分可显著提升字节对编码性能,但对无词边界无效。

针对具有复杂形态的语言(如泰卢固语),本文系统评估了不同分词算法(如字节对编码与无词边界)在小规模BERT模型上的表现,覆盖从预训练到微调的全过程。为衡量分词器的形态对齐能力,研究构建了一个包含600个派生词形和7000个屈折词形的金标准形态分割数据集。实验结果表明:第一,分词算法的选择是影响性能的最关键因素,无词边界分词在多数场景下持续优于字节对编码;第二,尽管更好的形态对齐与文本分类及结构预测任务性能呈中等正相关,但其影响远小于分词算法本身。值得注意的是,利用形态信息进行预切分能显著提升字节对编码的表现,但对无词边界分词无明显帮助。研究强调需建立更全面的内在评价指标以解释下游性能趋势。

原文摘要 · Abstract (English)

The relationship between tokenizer algorithm (e.g., Byte-Pair Encoding (BPE), Unigram), morphological alignment, tokenization quality (e.g., compression efficiency), and downstream performance remains largely unclear, particularly for languages with complex morphology. In this paper, we conduct a comprehensive evaluation of tokenizers using small-sized BERT models -- from pre-training through fine-tuning -- for Telugu (agglutinative), along with preliminary evaluation in Hindi (primarily fusional with some agglutination) and English (fusional). To evaluate morphological alignment of tokenizers in Telugu, we create a dataset containing gold morpheme segmentations of 600 derivational and 7000 inflectional word forms. Our experiments reveal two key findings for Telugu. First, the choice of tokenizer algorithm is the most significant factor influencing performance, with Unigram-based tokenizers consistently outperforming BPE across most settings. Second, while better morphological alignment shows a moderate, positive correlation with performance on text classification and structure prediction tasks, its impact is secondary to the tokenizer algorithm. Notably, hybrid approaches that use morphological information for pre-segmentation significantly boost the performance of BPE, though not Unigram. Our results further showcase the need for comprehensive intrinsic evaluation metrics for tokenizers that could explain downstream performance trends consistently.

分词算法形态学泰卢固语BERT

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