4.4 Variables and Functions
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Fig. 4.3 Fragment of VOV showing selected subclasses of vov:variable and the subclasses of
vov:function; the diagram was generated using the OWLViz protégé plugin; grey arrows labelled
“is-a” denote subsumption (), i.e. rdfs:subClassOf
• vov:variable: a variable in the mathematical sense, i.e. a symbol that stands for a
quantity in a mathematical expression.
• vov:function: a relation between two or more variables (e.g. the radial distribution
function, the energy density of states); it can be defined via a mathematical equation
or via tabulated values. Its subclasses (cf. Fig. 4.3) include vov:field.
Variables in VOV can be classified according to three main criteria: by their scope
(vov:object_variable, vov:pair_variable, vov:system_variable, vov:universal_variable),
their rank (vov:scalar_variable, vov:vector_variable, vov:tensor_variable) or their
basilar kind (vov:mass, vov:energy, …), for which qudt:QuantityKind is used [12]. In
Fig. 4.3, we show the splitting of vov:variable according to scope and the subclasses