Anything that has a URI, e.g. a class or property Anything that might have a URI, e.g. an individual Description-forming Operators Unordered sequence of Descriptions Unordered sequence of Descriptions with at least two Cardinality restriction The objectPropertyExpression group describes an object Property expression, e.g. a single property, inverse or composition. The dataPropertyExpression group describes an data Property expression, e.g. a single property or a chain. Pair of an object property and concept description or a data property and datatype Expression. Pair of Descriptions A pair of properties, either two object or two data. A collection of properties, all object or all data.