<?xml version="1.0" standalone="yes"?>
<Paper uid="P05-1010">
  <Title>Probabilistic CFG with latent annotations</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> This paper defines a generative probabilistic model of parse trees, which we call PCFG-LA. This model is an extension of PCFG in which non-terminal symbols are augmented with latent variables. Fine-grained CFG rules are automatically induced from a parsed corpus by training a PCFG-LA model using an EM-algorithm.</Paragraph>
    <Paragraph position="1"> Because exact parsing with a PCFG-LA is NP-hard, several approximations are described and empirically compared. In experiments using the Penn WSJ corpus, our automatically trained model gave a performance of 86.6% (Fa5 , sentences a6 40 words), which is comparable to that of an unlexicalized PCFG parser created using extensive manual feature selection.</Paragraph>
  </Section>
class="xml-element"></Paper>