Abstract: A computer-implemented method for synthesizing an operational ontology for a digital twin of a real or virtual entity which includes at least one data source. The method includes obtaining, using an extract transform load, ETL, system, data from the entity, as part of the ETL process, contextualising the obtained data using a plurality of specific ontologies. Each specific ontology includes one or more ontology fragments forming a set of characteristics for a data classification of the data from the entity. For each specific ontology, a representation of that specific ontology is used to contextualise a data classification of the data in a data store. An operational ontology for the entity is synthesized using the plurality of specific ontologies.