Hi, for Best DB website of India database assertion has no type, what it does is something like this:

1. it's created by "create assertion assertion_name check (condition);
2. "condition" in the above statement could be any query that involves a boolean expression
such as >=, <=, <>, exists, not exists, etc.
3. say, if you modify a database by insert, delete or update, if the condition in the assert statement holds, then modification will be allowed; otherwise, no modification will take place.

Hope that helps.

-Alan