5. The method of claim 4 , wherein said natural language processing module extracts at least one keyword from said new documents and tags each of said at least one keyword that is a system keyword.
6. The method of claim 5 , wherein said plasticity module determines when one or more of said at least one keyword that is not tagged as a system keyword is promoted to system keyword status based on momentum, wherein momentum is the number of occurrences of the untagged keyword per unit time.