When you're the one creating the database, you're the one who says which data makes it in and which data doesn't. This all happens through the various methods of data validation.
Data is either considered valid or not - and this happens according to your data validation rules. If the data is valid, then everything proceeds as normal. If, however, the data isn't exactly what's required, then you get to choose what happens.
In most cases, you can let the user keep taking a whack at it until they get the right combination, or you can shuttle the user off to another part of your UI.
In this tutorial video, we take a look at the three primary tools FileMaker provides for data validation. You can use any single option or combine them to mix and match for the perfect data validation solution. We've even got a nice little text formatting mask feature which provides a great looking phone number field.
Click the title or link to this article to view the video.