This paper presents a separation of concerns approach to solve the tangling problem of functional and Quality of Service (QoS) concerns in traditional Component-based Software Engineering (CBSE) and Software Product Line (SPL) technologies applied to Distributed Real-time and Embedded (DRE) systems. This problem originates from the interchangeability for fulfilling functional and QoS concerns during composition. The approach utilizes the perspective of QoS to design and analyze a set of software systems represented by a collection of QoS systemic paths, which determine how well functional tasks perform in terms of flows of application-specific and functionality-determined information between components. Our approach not only reserves the virtues of reusability, changeability, productivity and expeditiousness that traditional CBSE and SPL technologies possess, but also dedicates the contributions in terms of separation of concerns, design space exploration, fine-grained commonality...