Complex sentence: Google introduced their Knowledge Graph in 2012 by leveraging existing knowledge graphs, such as DBpedia and Freebase, and also opening the process for contributing to the graph by ingesting RDFa and microdata formats from indexed web pages, based on vocabularies published by schema.org.
Split into simpler sentences: Google introduced their Knowledge Graph in 2012 by leveraging existing knowledge graphs, such as DBpedia and Freebase. They opened up the process for contributing to the graph by ingesting RDFa and microdata formats from indexed web pages, based on vocabularies published by schema.org.