Evolution of cyber-physical systems (CPS) and extension of their application areas complicate, among other things, their software design and development. This requires improvements in programming techniques used to build CPS. One of the important tasks arising in complex CPS is a situation assessment (SA) based on data received from diverse sources. In the chapter, an ontology-driven approach for CPS SA software design and development automation is proposed. The approach is based on the JDL data fusion model and flexible enough to be applied for any class of CPS applications. In contrast to known approaches, ontologies are used not only for domain knowledge representation but also for SA calculation process formalization. It provides a higher level of automation of SA software synthesis and, in the end, increases design and development efficiency.