In this paper we present a new extensible model based upon the concept of subtransactions in real-time transaction systems. The nested transaction model originally proposed by J. Moss is extended for real-time uniprocessor transaction systems by adding explicit timing constraints. Based upon the model, an integrated concurrency control and scheduling algorithm is developed, that not only guarantees timing constraints of a set of real-time transactions but also maintains consistency of the database. The algorithm is based on the priority ceiling protocol of Sha et al. We prove that the Real-Time Nested Priority Ceiling Protocol prevents unbounded blocking and deadlock, and maintains the serializability of a set of real-time transactions. We use the upper bound on the duration that a transaction can be blocked to show that it is possible to analyze the schedulability of a transaction set using rate-monotonic priority assignment. This work is viewed as a step toward multiprocessor and distributed real-time nested transaction systems. Also, it is possible to be extended to include the real-time multimedia transactions in the emerging web-based database application areas.