Wireless sensor networks (WSN) imposes stringent constraints on efficiency, memory footprint and power consumption. Since the need to satisfy these constraints often results in tightly coupled designs, WSN applications tend to be inflexible; it is hard to flexibly reuse, introduce, customize and replace various non-functional properties (e.g., data routing, concurrency, data aggregation and event filtering) for developing and maintaining WSN applications. In order to address this issue, this paper proposes the TinyDDS middleware, which decouples various non-functional properties from WSN applications and allows those applications to flexibly reuse and transparently configure non-functional properties according to their own requirements. Without breaking the generic architecture of TinyDDS, the proposed pluggable framework allows WSN applications to have fine-grained control over non-functional properties and specialize in their own requirements. Currently, TinyDDS supports two types of non-functional properties: application-level and middleware-level non-functional properties.