from https://labs.etsi.org/rep/saref/saref-portal/-/issues/50 > Most SAREF extensions use W3C Time ontology, sometimes differently. > > It may be imported at the level of SAREF Core directly > > SAREF4AGRI uses the W3C Time ontology. It copies the definition of time:Instant, time:Interval, and time:TemporalEntity. Other SAREF ontologies use these concepts, therefore it could be useful to define them at the level of SAREF Core. and > Proposal: > > 1. SAREF Extensions should not promote the use of the W3C Time Ontology for time units over other ontologies of units of measure. > > 2. In SAREF Extensions, declare the concepts from W3C Time ontology that are needed, for example: > > ``` > time:TemporalUnit a owl:Class ; rdfs:isDefinedBy time: . > time:TemporalEntity a owl:Class ; rdfs:isDefinedBy time: . > ``` > > 3. SAREF Extensions should only declare the concepts that they use. > > 4. Favour xsd:dateTime and xsd:duration if modeling with DPs could be enough. Especially if only instants are expected.