1. WordNet: a lexical database for English;Miller;Commun. ACM,1995
2. Freebase: a collaboratively created graph database for structuring human knowledge;Kurt,2008
3. Yago: a core of semantic knowledge;Suchanek,2007
4. Knowledge vault: A web-scale approach to probabilistic knowledge fusion;Dong,2014
5. The SphereSearch engine for unified ranked retrieval of heterogeneous XML and web documents;Graupmann,2005