This paper presents a system, where a model of the user’s tasks is used for automatic service composition in smart spaces. In the system service modeling is decoupled from resource modeling. We present a model for quality of service (QoS) based service composition, integrating it with our resource management scheme. A component acting on behalf of the user composes the service with the aim of maximizing the QoS for the currently active user task. This functionality is decomposed to the description and determination of static and dynamic QoS. The concept of static QoS refers to the degree of match between the requirements of the user’s active task and the qualities and capabilities of a service composition. Dynamic QoS extends static QoS by taking into account the current state and availability of the resources.