11. The computer-readable storage medium of claim 1 wherein the operations further comprise: generating a hierarchical tree of the text-based terms in the collection, the hierarchical tree including a parent level and a child level, the parent level including a parent node representing a first unique text-based term in the ordered collection, the child level including at least one child node representing a second unique text-based term in the ordered collection document.
12. The computer-readable storage medium of claim 11 wherein the operations further comprise: maintaining a frequency of occurrence for each parent node in the parent level of the hierarchical tree, a frequency of occurrence for a given parent node being incremented for each detected occurrence of the first unique text-based term; and maintaining a frequency of occurrence for each child node in the child level of the hierarchical tree, the child frequency of occurrence for a given child node being incremented for each detected occurrence of the second unique text-based term.