Similarity Reasoning in Design Engineering Ontologies: A Conceptual Framework

Design engineering increasingly depends on the reuse of existing knowledge, yet this process is often hindered by heterogeneous information systems and inconsistent model representations. Ontologies provide a formal means to structure and connect such knowledge, enabling semantic reasoning across tools and disciplines. Among these reasoning capabilities, similarity assessment is essential for comparing, classifying, and reusing design concepts. However, existing approaches to similarity, whether structural, parametric, functional, or semantic, remain fragmented, domain-specific, and lack a common foundation. This paper reviews these classes of similarity and their use in design engineering, identifying how they capture different facets of engineering reasoning. Building on this analysis, it introduces a conceptual framework that integrates them within an ontological schema. The framework is structured as a three-step reasoning chain linking engineering intent, ontological representation, and computational mechanism. A mapping between semantic dimensions and computational techniques is proposed, together with a composite formulation combining geometric, parametric, functional, structural, and contextual similarity. The work provides a unified foundation for ontology-based similarity reasoning, supporting consistent method selection, design reuse, and product variant management.