The discovery, representation and reconstruction of Business Networks (BN) from Network Mining (NM) raw data is a difficult problem for enterprises. This is due to huge amounts of complex business processes within and across enterprise boundaries, heterogeneous technology stacks, and fragmented data. To remain competitive, visibility into the enterprise and partner networks on different, interrelated abstraction levels is desirable. We present a novel data discovery, mining and network inference system, called Business Network System (BNS), that reconstructs the BN--integration and business process networks--from raw data, hidden in the enterprises' landscapes. BNS provides a new, declarative foundation for gathering information, defining a network model, inferring the network and check its conformance to the real-world "as-is" network. The paper covers both the foundation and the key features of BNS, including its underlying technologies, its overall system architecture, and its most interesting capabilities.