1. A method of executing a query on linked data sources comprising: generating an instance graph expressing relationships between objects in said linked data sources; receiving a query including at least two terms; rewriting, heuristically, the query into an ordered list of sub-query terms, wherein the ordered list begins with first and second search terms; executing, with a processor, said first search term on said instance graph, wherein the execution outputs an execution result subset and wherein said executing said first search term further comprises performing a relationship search that ranks each object in said instance graph with respect to said execution result subset; generating a summary graph using the execution result subset, wherein objects having a score below a predetermined threshold are filtered out of said summary graph during said relationship search; aggregating to said summary graph two or more of said filtered out objects which are related to at least one object having a score above said predetermined threshold; and executing said second search term on said summary graph.