Most of the ORE systems utilize weak supervision knowledge to guide the extracting process, such as: Databases (Craven and Kumlien, 1999), Wikipedia (Wu and Weld, 2007;Hoffmann et al., 2010), Regular expression (Brin, 1999;Agichtein and Gravano, 2000), Ontology (Carlson et al., 2010;Mohamed et al., 2011) or Knowledge Base extracted automatically from Internet (Mintz et al., 2009;Takamatsu et al., 2012).
when iteratively coping with large heterogeneous data, the ORE systems suffer from the "semantic drift" problem, caused by error accumulation (Curran et al., 2007).