Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for identifying a group of related instance identifiers. In one aspect, a computer storage medium is encoded with a computer program. The program comprises instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations. The operations include receiving a search query at a data processing apparatus, the search query specifying attributes shared by a group of related instances, searching an electronic document collection to identify instance identifiers that are responsive to the search query, representing features of the instance identifiers in a vertex-edge graph, and scoring relevance of the instance identifiers to the search query according to the features represented in the vertex-edge graph.