Table 1
Summary of features provided by our representations. ∀a1[g(a)] represents a set of boolean features, one for each value of a, where the feature is true iff g(a) is true. xi represents a token at position i in sentence x, w represents a word type, Suffixes = {-ing,-ogy,-ed,-s,-ly,-ion,-tion,-ity}, k (and k) represents a value for a latent state (set of latent states) in a latent-variable model, y* represents the maximum a posteriori sequence of states y for x, yi is the latent variable for xi, and yi,j is the latent variable for xi at layer j. prefix(y,p) is the p-length prefix of the Brown cluster y.
| Representation | Features |
|---|---|
| Trad-R | ∀w1[xi = w] |
| ∀s ∈ Suffixes1[xi ends with s] | |
| 1[xi contains a digit] | |
| n-gram-R | ∀w′,w″P(w′ ww″) / P(w) |
| Lsa-R | ∀w, j {v′left(w)}j |
| ∀w, j {v′right(w)}j | |
| NB-R |  |
| Hmm-Token-R |  |
| Hmm-Type-R | ∀kP(y = k|x = w) |
| I-Hmm-Token-R |  |
| I-Hmm-Type-R | ∀j,kP(y.,j = k|x = w) |
| Brown-Token-R | ∀j ∈ {−2, −1,0,1,2} |
| ∀p ∈ {4,6,10,20} prefix(yi+j, p) | |
| Brown-Type-R | ∀p prefix(y, p) |
| Lattice-Token-R |  |
| Lattice-Type-R | ∀kP(y = k|x = w) |
| Representation | Features |
|---|---|
| Trad-R | ∀w1[xi = w] |
| ∀s ∈ Suffixes1[xi ends with s] | |
| 1[xi contains a digit] | |
| n-gram-R | ∀w′,w″P(w′ ww″) / P(w) |
| Lsa-R | ∀w, j {v′left(w)}j |
| ∀w, j {v′right(w)}j | |
| NB-R | |
| Hmm-Token-R | |
| Hmm-Type-R | ∀kP(y = k|x = w) |
| I-Hmm-Token-R | |
| I-Hmm-Type-R | ∀j,kP(y.,j = k|x = w) |
| Brown-Token-R | ∀j ∈ {−2, −1,0,1,2} |
| ∀p ∈ {4,6,10,20} prefix(yi+j, p) | |
| Brown-Type-R | ∀p prefix(y, p) |
| Lattice-Token-R | |
| Lattice-Type-R | ∀kP(y = k|x = w) |