A Character-based Approach to Distributional Semantic Models: Exploiting Kanji Characters for Constructing JapaneseWord Vectors

Many Japanese words are made of kanji characters, which themselves represent meanings. However traditional word-based distributional semantic models (DSMs) do not benefit from the useful semantic information of kanji characters. In this paper, we propose a method for exploiting the semantic information of kanji characters for constructing Japanese word vectors in DSMs. In the proposed method, the semantic representations of kanji characters (i.e, kanji vectors) are constructed first using the techniques of DSMs, and then word vectors are computed by combining the vectors of constituent kanji characters using vector composition methods. The evaluation experiment using a synonym identification task demonstrates that the kanji-based DSM achieves the best performance when a kanji-kanji matrix is weighted by positive pointwise mutual information and word vectors are composed by weighted multiplication. Comparison between kanji-based DSMs and word-based DSMs reveals that our kanji-based DSMs generally outperform latent semantic analysis, and also surpasses the best score word-based DSM for infrequent words comprising only frequent kanji characters. These findings clearly indicate that kanji-based DSMs are beneficial in improvement of quality of Japanese word vectors.