8. The computer program product of claim 6 , wherein to learn the sets of equivalent syntactic patterns further includes: receiving sets of related documents; determining, for each of the sets of related documents, expressions involving corresponding information; determining sets of equivalent syntactic patterns based on the expressions; and storing the sets of equivalent syntactic patterns in a data store.
8. The computer program product of claim 6 , wherein to learn the sets of equivalent syntactic patterns further includes: receiving sets of related documents; determining, for each of the sets of related documents, expressions involving corresponding information; determining sets of equivalent syntactic patterns based on the expressions; and storing the sets of equivalent syntactic patterns in a data store. 9. The computer program product of claim 8 , wherein the computer readable program, when executed on the computer, further causes the computer to: determine additional hidden syntactic patterns to include in one or more of the sets of equivalent syntactic patterns using a probabilistic model.