In order to achieve effective Digital Engineering solutions, it is necessary to solve the problem of integrating Product Lifecycle Management (PLM) and Model-Based Systems Engineering (MBSE) domains. Indeed, design processes are supported by a variety of ontologies representing each of the domains. Since none of the ontologies is sufficient on its own to describe the complete lifecycle, we propose an ontological engineering approach to model Engineering and Manufacturing data structures. In this paper, we address the fundamental issue of semantic integration of ontologies that can support Digital Engineering solutions. To achieve this goal, we define various types of interfaces between systems ontologies such as the Object-Process Methodology (OPM), the Core Product Model (CPM), and the Manufacturing Process Management (MPM). Revealing the connections between these ontologies has the potential to provide eventually more efficient management of all information throughout the entire product lifecycle. To accomplish this, we propose to use the fundamental OPM structural and procedural links that can be used to explicitly represent all causal interfaces within MBSE and PLM domains using the Design Structure Matrix (DSM)-based approach.