> How do I declare that in the database using IBExpert or EMS

IBManager ?

AddYear is not a built in function in Firebird. It is an external
function (UDF). In order to access an external function, your
database must contain the details of the function (what its called,
what parameters are there, what are the data types, how to clean up
memory, and which dll the function call is in). If your database does
not contain the declaration, you might as well be
calling 'FlyToTheMoon', because Firebird will have just as much idea
how that can be done.

Although AddYear is an external function, it is inside a library that
ships with Firebird. Specifically:

[Firebird install path]\UDF\fbudf.dll

There is a corresponding .sql file in the same folder that contains
the declarations. You just need to find the appropriate one and run
it (or just run the whole script).

But the rule is, if you haven't declared the external function inside
the fdb itself, you can't use it.

Adam