20. The computer-readable storage medium of claim 1 , the data structure further comprising a fourth table comprised of entries each representing a correspondence between two terms, each entry of the fourth table containing a first term ID identifying a child term, a second term ID identifying a parent term, and an indication of a relationship type that exists between the identified child term and the identified parent term.
20. The computer-readable storage medium of claim 1 , the data structure further comprising a fourth table comprised of entries each representing a correspondence between two terms, each entry of the fourth table containing a first term ID identifying a child term, a second term ID identifying a parent term, and an indication of a relationship type that exists between the identified child term and the identified parent term. 25. The computer-readable storage medium of claim 20 wherein a distinguished entry of the fourth table contains an indication that the identified child term references the identified parent term.