>Hi,
> How to return user defined error msg from trigger?

You can use ERROR "My Error message here". The error number will be 1098 (user defined error). You can trap for this and display your own message dialog or you can let VFP display your meessage in its error messagebox.

> Once I define relationship of tables, VFP add several stored procedure into my database. What soes those program does?
>

If you are talking about the referential integrity (RI) bulder then these are the stored procedures used by the database engine to maintain the integrity of your data by cascading updates and deletes, etc. They are called from triggers within your tables.