I agree completely with graff. Don't try to create a new language when an existing one will do nicely and especially not when using the existing language will result in less work both for you and your application.

If, however, you really feel that creating your own is a requirement—perhaps because some completely non-technical person will have to write or modify these condtions—I would suggest trying to avoid compounding words like 'indate' and 'notexist'. That's neither flexible nor very readable. Why wouldn't you use 'not exist' or 'in date' instead?

-sauoq
"My two cents aren't worth a dime.";