ways to detect that a table was changed ?

Hi, My application needs to refresh its copy of data if some tables are changed. Ideal solutions would be that: 1) Configure Informix to generate a Unix (or some kind of) signal to the applic. when a table(or column of a table) is modified -OR- 2) setup a trigger to run a unix program to generate signal to our applic. But I guess, informix doesn't support above schemes. Or does it ? Or, how about: 3)does informix provide timestamps of tables or columns so an applic. checks periodically if a table or a column was changed(just like timestamps of files)? If this is possible, where is this data in database and how to access it? Otherwise, my other crude options are: 4) define tables to hold timestamps, and setup triggers on every column of every table that needs to be monitored, and the triggers would fill these timestamp-tables which are periodically monitored by applic. 5) Not use create timestamp-tables but have applic. check periodically and do some in-direct processing (and I have few possible thoughts) like doing logical diffs on data etc. We are using informix 7.3 and solaris 2.6. (BTW, the applic. is in Java). Being able to detect a table change is also useful for administrators. Any opinions or experiences that you can share ? Thanks AH