Explanation on Mass Nouns

Mass nouns are terms such as 'water', 'gas', 'fuel', ...

They are part of oeo-physical because they are physical entities of the energy system domain.

Classification as Object Aggregate

It is possible to ask how much water there is, but not without asking e.g. how many litres of water there are. Thats why mass nouns are not singular objects but treated as object aggregate. E.g. the OEO considers not one singular "water" but portions of water. Mass nouns like "water" are therefore part of the OEO, but their definition should make clear, that the term refers to "a portion of" water, gas, air, etc. They are classified primarily as subclasses of the "Portion of matter" class.

Structuring the Portion of Matter Subclasses

For further structuring of the OEO equivalent classes are used. This way, more than one hierarchy can be implemented without hurting the monohierarchy principle. Some hierarchies that are currently implemented are:

• fuel: a hierarchy of all the fuels in the ontology
• greenhouse gases: a hierarchy of the greenhouse gases

Here, is also an issue discussing mass nouns inside the OEO.