[TYPO3] How to validate database record fields upon entry

[Henry]

Greetings.

I've been developing an extension for publishing KML-files used by Google
Earth from TYPO3. It's currently in the early alpha stage.

The problem is, that Google Earth is really picky about the data it parses.
For example, longitude and latitude values should consist of 16 digits,
otherwise Google Earth might not show them at all. The user entering the
data, however, should be able to enter a value like "37.4" instead of
"37.42244015321688".

I've been trying to figure out how to validate entered records immediately
after they are entered, but so far I haven't found anything useful about the
subject. At the moment I've built a workaround which validates and reformats
the data every time it is fetched from the database, but this is quite an
unefficient solution.

Is it possible to somehow validate the database records when they are
entered? I'm a new user to TYPO3, so please excuse me if I have missed
something really basic here...

Thanks,
- Henry