“…16 articles introduce data transformations or align them with a mapping language for heterogeneous (semi-)structured data [99,86,38,132,87,107,70,73,32,15,90,41,40,95,39,7]. 21 articles describe a materialization system [85,86,30,132,107,122,87,83,81,115,45,72,54,46,114,120,64,51,98,96,116], and 18 articles a virtualization system for transforming heterogeneous (semi-)structured data into a knowledge graph [99,104,19,89,126,26,18,48,75,112,22,13,76,…”