Implementation of data-based key performance indicators (KPIs) within existing plants usually requires a thorough manual analysis of the plant topology to define which sensors could provide reliable information for calculating the KPIs. In this publication, we propose an assistance system that automates this process. First the automatic linkage between plant structure and operational data is presented for the evaluation of the process efficiency. Next, a concept and prototypical implementation of the evaluation of predefined KPIs is described. The plant structure is described according to the DEPXI specification, while a rule-based framework was developed to depict the process-engineering knowledge. The proposed methods have been validated in an experimental setup. It could be shown that with standardized inputs, a generic extendable evaluation of the plant performance can be achieved.