Public communication during natural and man-made disasters is a key issue that must be addressed to protect lives and properties. The choice of the best protective actions to take depends on a global situation-awareness that is not available to the general public. Emergency personnel and public authorities have the duty to inform the population before, during and after catastrophic events to support the disaster response. In this paper we describe the design and the implementation of PWS (Policy-driven Warning System), a system for public warning dissemination. PWS is not intended to replace existing systems or procedures, but to serve on top of them in order to leverage the current emergency response knowledge.