A new quorum-based replica control scheme for managing replicated data in distributed systems is proposed. We first introduce a concept called relaxed difference pair to establish the basics for cyclic read-write coteries. A simple and efficient model is then presented to facilitate the construction of read-write coteries. The read-write coteries generated by the model are symmetric. The proposed scheme can be applied to arbitrary number of data copies. More importantly, by introducing a parameter in the construction model, our scheme provides the exibility of adjusting the sizes of read and write quorums. Such exibility allows one to construct a read-write coterie that best suits the environment of the target system.