1. A computer system comprising: memory storing a first source data graph in a first identifier space; memory storing a reconciled version of a second source data graph, the second source data graph being in a second identifier space and the reconciled version of the second source data graph being in a third identifier space; memory storing a master evidence file that maps the first identifier space to the third identifier space and the second identifier space to the third identifier space; at least one processor; and memory storing instructions that, when executed by the at least one processor cause the system to: generate a reconciled version of the first source data graph by substituting identifiers in the first source data graph with identifiers in the third identifier space using the master evidence file, store the reconciled version of the first source data graph, and generate a combined data graph from the reconciled version of the first source data graph and the reconciled version of the second source data graph, the combined data graph being available for querying.