The Semantic SI Ontology: Engineering, Alignment, and Validation of a Semantic SI Model

Abstract

The Semantic SI Ontology (SIS) provides a semantic model for representing the value of a physical quantity, including kind of quantity, International System of Units (SI) measurement unit, and measurement uncertainty, in accordance with the official Bureau International des Poid et Mesures (BIPM) recommendations. Developed as a formal counterpart to the Digital System of Units XML schema definition (D-SI XSD), the ontology enables harmonized, machine-readable, and interoperable representation of metrological data. This paper outlines the design rationale, the transformation methodology from eXtensible Markup Language (XML) Schema to Web Ontology Language (OWL), and its alignment with existing semantic standards such as Quantities, Units, Dimensions, and Data Types Ontologies (QUDT) and the SI Reference Point. Core ontology structures - such as QuantityValue and MeasurementUncertainty - are discussed in detail. The paper also presents the validation framework, including a Python toolc hain for generating OWL individuals from XML, Shapes Constraint Language (SHACL)-based shape validation, and reasoning with established OWL reasoners. Applications in ongoing projects, such as the Metadata4Ing and the Digital Calibration Certificate (DCC) ontology, demonstrate the practical relevance of the SIS as a foundational component in the digital transformation of metrology.