18. The computer program product as in claim 17 further including instructions to support operations of: maintaining positional information for each parent node, the positional information providing a mapping to a location in the ordered collection where a corresponding parent text-based term is located; and maintaining positional information for each child node, the positional information providing a mapping to a location in the ordered collection where a corresponding child text-based term is located.
17. The computer program product as in claim 16 further including instructions to support operations of: creating the tree such that the parent node represents a first word and the child node represents a second word, a combination of the parent node and the child node representing a phrase including the first word and the second word.