The simplest subgraph uses a first-order factorization (McDonald et al., 2005) which decomposes a dependency tree into single dependency arcs ( The most common choice for ScoreF (x, c; θ), which is the score function for subgraph c in the tree, is a simple linear function: where f (x, c) is the feature representation of subgraph c and w is the corresponding weight vector.
the effectiveness of this function relies heavily on the design of feature vector f (x, c).