21. The apparatus of claim 15 , further comprising: a module for periodically checking for free space in said UDB and, if said free space is less than a predetermined amount, then removing from said UDB said frequency counts and corresponding object numbers or corresponding user-defined words for words that have frequency counts below a predetermined threshold.
21. The apparatus of claim 15 , further comprising: a module for periodically checking for free space in said UDB and, if said free space is less than a predetermined amount, then removing from said UDB said frequency counts and corresponding object numbers or corresponding user-defined words for words that have frequency counts below a predetermined threshold. 22. The apparatus of claim 21 , wherein said removing module removes user-defined words having frequency counts below said predetermined threshold after removing other words having frequency counts below said predetermined threshold.