1. A method in a computer system for performing a relationship search of a corpus of documents, each document having at least one sentence, comprising: receiving a relationship search query that designates a desired grammatical relationship between a first entity and at least one of a second entity or an action; transforming the search query into a Boolean expression; under control of the computer system, automatically determining a set of data objects that match the Boolean expression using a keyword-style search of a data structure that indexes terms of the documents in a memory of the computer system by including, for at least some of a plurality of terms, grammatical relationship information that specifies that the corresponding term is a subject, object, or modifier of another term, and including for at least one of the plurality of terms having the included grammatical relationship information, semantic information that specifies an entity type that identifies the term as a type of person, location, or thing; when the received relationship search query designates a desired grammatical relationship between the first entity and any action, returning an indication of a plurality of matching objects in the corpus that encompass the first entity along with an indication of the corresponding action encompassed by the matching objects; and otherwise, returning an indication of a plurality of matching objects in the corpus that encompass the desired grammatical relationship.