As system complexity has increased, so has interest in reusing software components in early development phases. While most current modeling methods support design of generic parameterized frameworks or patterns and weaving them into specific models, they do not support open reuse, i.e., the ability to develop partially specified components and refine them in the target application. We introduce an open reuse formalism that is based on OPM/Web, an extension of Object-Process Methodology for distributed systems and Web applications. Our open reuse is accomplished by a three-step process, consisting of designing reusable models, creating basic woven models, and enhancing their specification. We model a reusable component through partially specified environmental elements that are bound to concrete counterparts when the component is integrated into the system under development. Rules for modeling and combining components are defined and applied to a Web example.