SDN simpli??~Aes network management by relying on declarativity (high-level interface) and expressiveness (network ??~Bexibility). We propose a solution to support those features while preserving high robustness and scalability as needed in carrier-grade networks. Our solution is based on (i) a two-layer architecture separating connectivity and optimization tasks; and (ii) a centralized optimizer called DEFO, which translates high-level goals expressed almost in natural language into compliant network con??~Agurations.