Monitoring systems can become more robust, flexible, scalable and smart through the implementation of a smart software layer. Such a software can be termed as middleware as it filters and provides data to applications and is independent of how data is propagated from source to a remote data-repository such as a database. The data is collected from a set of possibly heterogeneous sensors, among which some sensors can have processing capabilities to run the proposed middleware. Smart-rules are used to process and filter the sensed data and to initiate appropriate reactive routines according to the sensed data. All these features, make the proposed middleware as a smart-middleware. The capable sensors with such a smart-middleware can filter data according to smart rules. Additionally, with the help of the proposed smart-middleware, the capable sensors can collect, filter as well as aggregate data from other sensors in a hierarchical manner. This also results in reduced data volume and overall power consumption to process this data. Complemented with smart algorithm for fault tolerance and scalability, this paper presents the architecture of a middleware for smart monitoring systems in green data centers.