Cloud-of-things service providers use various descriptions languages to describe Quality of Service (QoS) attributes. However, existing modelling approaches provide support for modelling static QoS attributes only and lack features to model and reason with dynamic QoS attributes such as response time and availability. This paper presents an event-based approach for monitoring dynamic QoS values and their compliance by modelling the behavior of QoS attributes using an Event Calculus (EC) based framework. The logic based reasoning is then performed to proactively identify the possible QoS violations in future.