The paper considers compositional scheduling for hierarchical real-time systems using periodic resource models, which has been extensively studied in the past. We identify an unrealistic assumption in the existing literature that can make the computed component interfaces unimplementable. Namely, resource bandwidth can be expressed using arbitrary rational numbers. We show that resource bandwidth, computed by an algorithm that removes this assumption becomes overly pessimistic, and offer a new notion of a dual-periodic resource model (DPRM) interface that improves resource bandwidth of the interface. We study composition using DPRM interfaces and show properties of the new approach in terms of required resource bandwidth and preemption overhead.