Reliably producing software architectures in selected architectural styles requires significant expertise yet remains difficult and error-prone. Our research goals are to better understand the nature of style-specific architectures, and relieve architects of the need to produce such architectures by hand. To achieve our goals, this paper introduces a formally precise approach to separate architectural style design decisions from application-specific decisions, and then uses these separate decisions as inputs to an automated synthesizer. This in effect supports a model-driven development (MDD) approach to architecture synthesis with style as a separate design variable. We claim that it is possible to formalize this separation of concerns, long implicit in software engineering research; to automatically synthesize style-specific architectures; and thereby to improve software design productivity and quality. To test these claims, we employed a combination of experimental systems and case study methods: we developed an MDD tool and used it to carry out case studies using Kitchenham's methods. Our contributions include: a theoretical framework formalizing our separation of concerns and synthesis approach; an MDD framework, Monarch; and results of case studies that we interpret as supporting our claims. This work advances our understanding of software architectural style as a formal refinement; makes application descriptions an explicit subject of study; and suggests that synthesis of architectures can improve software productivity and quality.