“…Over 80% of data in the World Wide Web (WWW) are present in the form of an unstructured or semi-structured type, which makes knowledge extraction one of the major challenges in the KG research community. Fifteen years ago, researchers at the University of Twente and the University of Groningen, Netherlands, initiated the researches on KG theory and continued its focus on KG applications to analyze a text [5]. Over the years, several open KBs or ontologies have been created, including WordNet, DBpedia, YAGO, Freebase, BabelNet, and NELL, covering millions of real-world entities and relations in different domains [3,10,11,13].…”