Self-Management of multiservice network domains must include automatic detection of service quality violations in order to perform appropriate and timely responses, fostering the fulfillment of the service agreements committed with customers, or other ISPs. As knowledge based systems are capable of emulating human knowledge, they are presented here as convenient tools to specify heuristics for QoS violation detection. In this paper, the implementation of a service violation detection agent is described and an illustrative scenario of its use is also presented. Key words: Service Level Specification, Knowledge based Systems, Quality of Service, Self-configuration Networks.