In Service Oriented Computing (SOC), modeling the Quality of Service (QoS) is a cornerstone for providing services with quality guarantees. As the technological advances and wide adoption of handheld devices (e.g., PDA and smartphones) and wireless networks (e.g., UMTS, WiFi and Bluetooth) have made service environments more dynamic, QoS models must change accordingly. In this paper, we present a QoS model that provides the approporiate ground for QoS engineering in SOC. Our model focuses on emerging QoS features related to the dynamics of service environments such as user mobility and context awareness of application services. It also considers QoS on an end-to-end basis by covering QoS features of all the resources and actors involved in service provisioning (e.g., network, device, service, end-user). Our model represents QoS with rich semantic information and makes use of the Web Service Quality Model (WSQM) proposed by OASIS.