Taxonomies, which serve as backbones for structured knowledge, are use-ful for many NLP applications such as question answering (Harabagiu et al., 2003) and document clustering (Fodeh et al., 2011).
handcrafted, well-structured taxonomies such as Word-Net (Miller, 1995), OpenCyc (Matuszek et al., 2006) and Freebase (Bollacker et al., 2008), which are publicly available, can be incomplete for new or specialized domains.