Combating the Sparse Data Problem of Language Modelling

The talk will concern several ideas that combat the sparse data problem of language modeling. All alleviate it, neither solves it. These ideas are: equivalence classification of histories, positional clustering (different cluster systems for different n-gram positions), use of linguistic classes (e.g., Wordnet), class constraints in maximum entropy estimation, random forests, and neural network classification. An interesting problem that must be faced is as follows: words that are sparse and need to be classified do not have sufficient statistics to indicate their appropriate class membership.