. . . . . "Property values usually appear in groups which are called value structures, value spaces or measurement systems.\nEach of these structures corresponds to some property. More intuitively, one could say that the property may be measured with respect to some measurement system.\nFor instance, sizes may be measured with the values ``small'' ``big'' or ``very big'', which are the elements of one value structure.\n\nThe notion of a value structure of a property is similar to a quality dimension in (Gardenfors, 2000).\n\nFurther, value structures are related to quality spaces in DOLCE (Masolo, 2003}. A quality space consists of all ``quales'' (our property values) of some ``quality'' (our property).\n\nOften it seems to be the case that a notion of distance can be defined, and that certain layers of value structures are isomorphic to some subset of real numbers, which allows for a mapping of values to pairs of a real number and a unit, as in the case of ``10 kg''."^^ .