these two are SQL concepts

TRigger is a special type of stored procedure that

automatically takes effect when the data in a specified

table is modified.

triggers invoked in response to an INSERT,UPDATE OR DELETE

STATEMENT EXECUTED.

TRIGGERS are used to handle some exceptional conditions

if u r moving data 40 MB into data base,But data base having

only 30 mB free space then the trigger fires automatically

and the entire transaction automativcally roll backs.

Rules:

Rules are database objects used to enforce data integrity.

this object bound to column or userdefined data types.

to ensure that only valid values are allowed to insert in

to columns.

so trigger acts automatically nad rollbacks the transaction

when error is occured.

rule is used to enforce data integrity on a column or user

defined data type.