Objectives: To demonstrate how a transition to an open hospital information system architecture can help foster stronger collaborations between computer-based clinical tools and the network of care process stakeholders. Methods: Description of two evolution strategies towards an open, component-based architecture: the vertical decomposition of a monolithic system, and the transversal integration of foundation components such as terminology servers, documentation management, prescription, scheduling, workflow and notification engines. Conclusion: The progressive migration of production clinical systems towards a component-based architecture is feasible at a reasonable cost and leads to substantial benefits in terms of user acceptance through participative design and collaborative maintenance of knowledge bases, as well as improved ability to evolve, scale and share individual components. A taxonomy of the components of a health information system and their interactions should be developed to realize the collaborative potential of a marketplace of interoperable components.