17. The method of claim 14 further comprising maintaining a frequency counter for each parent node in the tree, a frequency counter of a given parent node being incremented when the respective first term is found in a grouping of the ordered collection; and maintaining a frequency counter for each child node in the tree, the frequency counter of a given child node being incremented for each detected occurrence of the respective second text-based term in the ordered collection that immediately follows an occurrence of the first text-based term of the given grouping.
14. A method comprising: receiving a collection of text-based terms; analyzing groupings of consecutive text-based terms in the collection to identify occurrences of different combinations of text-based terms in the collection; based on the analyzing, creating a tree in which a first term in a given grouping of the groupings is defined as a parent node in the tree and a second term in the given grouping is defined as a child node of the parent node in the tree; and maintaining frequency information representing the occurrences of the different combinations of text-based terms in the collection.