Digital System of Units
D-SI
FAIR data formats, services, and tools building an anchor of trust for processing international units of measurement in digital applications for science and technology.
Status: Foundational technology, steadily growing tool stack
D-SI Metadata Model and implementations
PTB’s D-SI metadata model provides universal, easy-to-use, unambiguous, and safe building blocks for the digital representation and exchange of metrological data. Machine- and human-useable reference implementations of these building blocks are provided for formats XML SCHEME, JSON LINKED DATA and Semantic-Web compatible Ontologies.
D-SI Metadata Model
Common conceptual models for metrological data and associated metadata based on recommendations from the International System of Units and metrological guidelines.
Version: 2 (long term stable)
D-SI XML Scheme
XML Implementation of D-SI
Version: 2.2.1(long term stable)
SIS Ontology
OWL Ontology implementation of D-SI in RDF (TURTLE)
Version: v0.2.1(beta)
D-SI LD
JSON-LD implementation of the D-SI, linking XSD and Ontology (provided as JSON-LD context file)
Version: 2.2.1 (beta, linked to XML Schema version)
Interoperability Framework
Based on Resolution B of the 27th CGPM on the global Digital Transformation of the International System of Units, the D-SI is fostering interoperability of measurement data across digital developments of an international scientific and quality infrastructure. Data, services, and tools are enabled to access an internationally established Interoperability Framework.
D-SI Converter (DME)
Software libraries, command-line-service and web-service for conversion between units and unit representation systems. This service is a Digital Metrological Expert tool. It supports automated conversion and provides metrologically traceable reports for results of conversions.
(Project start February 2026)
Legacy work such as the
SI Reference Point to D-SI transfromer
and the
are being harmonized with this work.
D-SI Constants
Web service providing values of physical and mathematical constants in the D-SI XML format. This service concludes legacy work from project SmartCom D-SI-based list of constants
BIPM SI Reference Point
Official international digital reference for the definition of the SI. Developped and operated by the BIPM. Used as reference for D-SI units.
Version 1.0.5 beta
IEC-CDD Units of Measurement Dictionary
Registry of units of measurement used as D-SI reference for conversion data.
Version 2.0018.0002
QUDT Ontology
Registry of units of measurement and kinds of quantities. D-SI references of units and kinds of quantities in ontologies.
Version 3.2.1