Introduction

Abstract

Though the phrase “knowledge graph” has been used in the literature since at least 1972 [Schneider, 1973], the modern incarnation of the phrase stems from the 2012 announcement of the Google Knowledge Graph [Singhal, 2012], followed by further announcements of the development of knowledge graphs by Airbnb [Chang, 2018], Amazon [Krishnan, 2018], eBay [Pittman et al., 2017], Facebook [Noy et al., 2019], IBM [Devarajan, 2017], LinkedIn [He et al., 2016], Microsoft [Shrivastava, 2017], Uber [Hamad et al., 2018], and more besides. The growing industrial uptake of the concept proved difficult for academia to ignore: more and more scientific literature is being published on knowledge graphs, which includes books (e.g., Fensel et al. [2020], Kejriwaletal. [2021], Pan etal. [2017], Qi etal. [2020]), as well as papers outlining definitions (e.g., Ehrlinger and Wofi [2016]), novel techniques (e.g., Lin et al. [2015], Pujara et al. [2013], Wang et al. [2014]), and surveys of specific aspects of knowledge graphs (e.g., Paulheim [2017], Wang et al. [2017]).