WEB Ontological representation of materials quantities and unitsWednesday (01.01.2020) 00:45 - 01:00 Part of:
The European Materials & Modelling Ontology (EMMO)  is a multidisciplinary effort to develop a standard representational framework based on physics and physical sciences, analytical philosophy and information technology. It is intended to be the bases for a hierarchical structure of domain and application ontologies enabling semantic interoperability. A common reference for physical quantities and units is an essential step towards true interoperability needed for efficient coupling different materials models and characterisation techniques. The common middle level EMMO ontology therefore include an extendable set of basic physical quantities based on the ISO 80 000 standard .
A quantity is in EMMO described using the concept of symbols and formal languages. It is a formal language with two spatial direct paths; a numerical (number or array of Boolean/integer/real/...) and a reference unit. Physical quantities are also mathematical objects and restrict the reference unit to only measurement units. They can be categorised to be either base quantities or derived quantities in a given unit system (the middle level EMMO ontology relies on the International System of Quantities (ISQ), which underlies the SI system).
Physical quantities are related to units via the physics dimension of the unit. This is an open-ended approach that allows to measure a quantity with new units added by a domain or application ontologies. It also allows automated consistency checking and dimensional analysis. Units are categorised into prefixed and non-prefixed units, where prefixed units are units that is made of a metric prefix and a unit symbol, while non-prefixed units do not have a metric prefix. Another useful categorisation is homogeneous (units with a pre-factor of one when expressed in base SI units) and non-homogeneous units, which allows for automated unit conversions.
Domain and application ontologies are expected to further specialise the included physical quantities by subclassing, to provide an exact definition of the quantities they deal with. Interoperability between domain or application ontologies may require mappings and sometimes also transformations. The ontology can say when this is needed and what transformations that are available.