Finding out when a row in a table was last changed.

I need to know when a (field in a) row in a table was last updated, but I want to avoid adding a timestamp field to the table for reason of software version enhancement and fallback issues. Does any one know of a fairly efficient inherent informix feature that I could use to achieve this? Can it be turned on in queries or on creating/altering parts of the existing schema per table, or even per column if possible ? I cannot make changes to the server's configuration. Even if it could be turned on by adding a constraint or something. It may create few enhancement/fallback issues if left in a version of the database accessed by an earlier version of the software that didn't make use of the feature, apart from a performance issue trhat would be in the future versions anyway. Many thanks, Andrew. sending to informix-list