Latent-Variable PCFGs: Background and Applications

Latent-variable probabilistic context-free grammars are
latent-variable models that are based on context-free grammars.
Nonterminals are associated with latent states that provide
contextual information during the top-down rewriting process of
the grammar.
We survey a few of the techniques used to estimate such grammars
and to parse text with them. We also give an overview of what the latent
states represent for English Penn treebank parsing, and provide
an overview of extensions and related models to these grammars.