1. A method for monitoring a system which includes a plurality of nodes coupled by a network, the method comprising: managing a first rule which has at least one first relationship between a first condition element and a first conclusion element and a second rule which has at least one second relationship between the first condition element and a second conclusion element, the first relationship and second relationship being configured by considering a topology of the system; creating a data structure including a first cause object corresponding to the first conclusion element in the first rule, and a second cause object corresponding to the second conclusion element in the second rule, and a first condition object corresponding to the first condition element in both the first rule and the second rule, the first condition object being linked to both the first cause object and the second cause object without duplication of the first condition object; and analyzing a root cause of an event, which has occurred on a node of the system and is related to the first condition object, based on the data structure.