In this paper, the formalized description of active rules in ORDBMS (object-relational database management system) is presented. The semantics of rule components, rule inheritance, rule operations, multiple rule triggering and rule cascade triggering is fully discussed. And a simplified E-C-A (event-condition-action) model called S E-C-A model suited to ANGEL system is achieved. Four types of rules (update-update rules, update-query rules, query-update rules and query-query rules), C-A coupling mode and priority definition of conflicting triggers are supported in S E-C-A. The capabilities of express and actualize set constraints are gained by extending NEW and OLD to a kind of path quantifier in expression forms of trigger constraint. And the analytic methods of rule behaviors based on transaction are also presented.