Abstract: Event is a human knowledge unit with larger-grained than concept．It is closer to the human cognitive process．As an important element of the event,action describes the process of status change of the objects in the event．Adding time to the process of status change,and describing action as the process of object''s status change with time,lead to a more specific description of action．This paper constructed an action formalism through actions,objects and time in the event,and studieds the syntax and semantics of certainty action and uncertain action．This action formalism combines an extended description logic with time (T-ALC) with logic program,thus to enhance the expressive ability of action．In this action formalism,the certainty actions forms are transformed to Datalog rules based forms to realize dynami-cal reasoning,and uncertainty action forms are transformed to Datalog rules based forms to realize uncertainty reasoning．At last,a case study of bank service was described to verify the feasibility of the action formalism and reasoning method.

Key words: T-ALC,Logic program,Event action,Action reasoning,Uncertainty reasoning