The connectivity between shop floor automation devices (OT level) and management systems (IT level) is becoming an essential research and innovation aspect that needs to be demonstrated with Technology Readiness Level six (TRL 6) and higher to make the Industry 4.0 paradigm an industrial reality. This paper describes the building of an Industry 4.0-compliant lab environment, which consists of a service-oriented shop floor (OT level) and three major management systems: an ERP system; a database; and a simulation for predictive maintenance (IT level). The architecture of the system follows the ISA'95 standard enterprise architecture, e.g. by assigning the components of the system to the corresponding levels of the ISA'95 model. A middleware acts as a common interface between these systems. Basic requirements for this middleware are interfaces to the lower level systems via OPC-UA and upper level systems by accessing a database. The middleware should be translated the data follows soft real-time requirements. This manuscript presents the major aspects that need to be taken into account for the selection of adequate industrial middleware, e.g. defining exactly which kind of data needs to be exchanged and with which semantics this data is going to be represented.