1. A computer system for identifying flee-text documents, the system comprising: a knowledge source storing in a knowledge database a plurality of concepts formed based on one or more words from a predefined vocabulary set, the knowledge source maintaining a plurality of relationship links wherein each relationship link defines a relationship between a first semantic grouping of the concepts and a second semantic grouping of the concepts; an input receiving an input query including an original query concept and at least one scenario identifier, the at least one scenario identifier being associated with at least one of the relationship links; a database of flee-text documents, wherein each document is indexed via one or more indexing concepts formed based on one or more words from the predefined vocabulary set; one or more processors coupled to the input, each of the one or more processors being operable to execute one or more computer instructions which: generate the indexing concepts for the free-text documents based on the one or more words from the predefined vocabulary set, wherein the program instructions which generate the indexing concepts include computer instructions for: maintaining a plurality of data structures mapping each of the plurality of concepts in the knowledge source to all words appearing in the concept; receiving a particular one of the free-text documents; identifying based on the plurality of data structures the one or more of the plurality of concepts in the knowledge source mapped to a set of words appearing in the particular one of the free-text documents; and returning the one or more identified concepts as candidate index concepts for the particular one of the free-text documents; automatically generate an expanded input query including both the original query concept and one or more additional query concepts, the one or more additional query concepts being selected from one or more first particular semantic groupings of the concepts in the knowledge source that have a specific relationship link with a second particular semantic grouping of the concepts containing the original query concept, the specific relationship link being identified by the at least one scenario identifier, wherein the computer instructions which automatically generate the expanded input query further include computer instructions which: filter candidate expansion concepts not included in the one or more first particular semantic groupings of the concepts in the knowledge source; and return the one or more additional query concepts based on the filtering; compare the expanded input query with the indexing concepts for the free-text documents; and return one or more of the free-text documents that satisfy the expanded input query based on the comparison.