The only thing I got out of your example in relation TDB 4, is loss of data.  I'm not exactly why you would want to cut off ends of records or data.  Also, I don't know what filter system you are talking about in the TDB.  Unless you are talking about verifying a field's field type (i.e. ID, number, memo), which is in the add() function.

Oooh, I think I understand now...

Basically he suggests having a list of expressions or something to be automatically run as data is inserted into the database. These expressions could be added to the script dynamically at run time. (Not sure if this is actually a better description at all :|)

Actually jono, correct.

You can modify the data before passing it as an argument to a method in the TDB.  That or you could extend the TDB class, making the same methods in the extended class, then reference the original TDB method.  Basically, we'd like to keep the TDB as bare with very little unnecessary coding as possible.