Why does extracting probabilistic context-free grammars (PCFGs) from a large, automatically parsed corpus for use in a statistical machine translation (SMT) system often lead to suboptimal translation performance?

💡 Explanation

The performance suffers because parse errors within the corpus, propagated through the grammar extraction process, introduce inaccuracies into the PCFGs. This error propagation adversely affects translation quality; therefore, the PCFG becomes unreliable, rather than reflecting true language patterns or lacking other features.

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