BPEL is emerging as an open-standards language for Web service composition. However, its procedural style can lead to inflexible and tangled code for managing a crosscutting aspect ? synchronization constraints that define permissible sequences of execution for activities in a process. In this paper, we present DSCWeaver, a tool that enables a synchronization-aspect extension to BPEL. It uses DSCL, a synchronization expression language, to specify constraints. DSCL has the desirable features of declarative syntax, fine granularity, and validation support. A designer can use DSCL to describe and validate the synchronization behavior and rely on DSCWeaver to generate BPEL code. We demonstrate the advantages of our approach in a service deployment process and evaluate its performance using two metrics: Lines of Code (LoC) and Places to Visit (PtV). Evaluation results show that our approach can effectively reduce development effort of process designers while providing performance competitive to un-woven BPEL code.