7. A system comprising: one or more computers configured to perform operations comprising: identifying, by one or more of the computers, an entity reference in a knowledge graph, wherein the entity reference corresponds to an entity type; identifying, by one or more of the computers, a missing data element associated with the entity reference, the missing data element reflecting a property of the entity reference for which no property value is currently assigned; generating, automatically by one or more of the computers in response to identifying the missing data element associated with the entity reference, a query based at least in part on the missing data element and the entity type; providing, by one or more of the computers, the query to a query processing engine; receiving information from the query processing engine in response to the query; and updating, by one or more of the computers in response to receiving information from the query processing engine, the knowledge graph based at least in part on the received information.
7. A system comprising: one or more computers configured to perform operations comprising: identifying, by one or more of the computers, an entity reference in a knowledge graph, wherein the entity reference corresponds to an entity type; identifying, by one or more of the computers, a missing data element associated with the entity reference, the missing data element reflecting a property of the entity reference for which no property value is currently assigned; generating, automatically by one or more of the computers in response to identifying the missing data element associated with the entity reference, a query based at least in part on the missing data element and the entity type; providing, by one or more of the computers, the query to a query processing engine; receiving information from the query processing engine in response to the query; and updating, by one or more of the computers in response to receiving information from the query processing engine, the knowledge graph based at least in part on the received information. 8. The system of claim 7 , wherein identifying a missing data element comprises: comparing properties associated with the entity reference to a schema table associated with the entity type; and determining that the schema table includes the property of the entity reference for which no value is currently assigned.