Although reuse is the main goal of SOA, composing existing services to realize different user requirements is still a difficult and time-consuming task. Research on workflow templates and design patterns can facilitate reuse and assist with the service composition task. Nevertheless, workflow templates are too specific, whereas design patterns may be too abstract; their effectiveness in assisting the composition process may be limited. In this paper, we propose a comprehensive service pattern model that is more flexible than workflow/service templates while allowing systematic instantiation into the concrete workflows. It can help ease the composition process and enable flexible pattern-based reuse.