A relational database is a database that explicitly stores information on relations between entities that are significant in our model. While regular training data allows the model to infer and learn relationships, a relational database explicitly states the relations significant for the problem at hand.

A knowledge base is any database intended to convey "commonsense" knowledge that humans normally know from day-to-day experiences for a deep learning model. Significant knowledge bases include Freebase, OpenCyc, WordNet, Wikibase, and GeneOntology.