15. The method of claim 14 further comprising 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.
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.