We show the statistics of the dataset we use in tab:statistics, and the construction procedures will be introduced in this section. In Wikidata BIBREF8 , facts can be described as (Head item/property, Property, Tail item/property).  We first choose the most common 202 relations and 120000 entities from Wikidata as our initial data. ReVerb BIBREF9 is a program that automatically identifies and extracts binary relationships from English sentences. We use the extractions from running ReVerb on Wikipedia. FB15K BIBREF3 is a subset of freebase. TACRED BIBREF10 is a large supervised relation extraction dataset obtained via crowdsourcing. We directly use these two dataset, no extra processing steps were applied. 
 Question: Which knowledge bases do they use?
Wikidata ReVerb FB15K TACRED