Number (19 kinds, 108 facts) - A measure of how many things there are, or how much there is, of a certain kind. Numbers are subclassed into RealNumber and ComplexNumber (ImaginaryNumber is an instance of Number)
PhysicalQuantity (127 kinds, 524 facts) - A PhysicalQuantity is a measure of some quantifiable aspect of the modeled world, such as 'the earth's diameter' (a constant length) and 'the stress in a loaded deformable solid' (a measure of stress, which is a function of three spatial coordinates). All PhysicalQuantities are either ConstantQuantities or FunctionQuantities. Instances of ConstantQuantity are dependent on a UnitOfMeasure, while instances of FunctionQuantity are Functions that map instances of ConstantQuantity to other instances of ConstantQuantity (e.g., TimeDependentQuantities are FunctionQuantities). Although the name and definition of PhysicalQuantity is borrowed from physics, PhysicalQuantities need not be material. Aside from the dimensions of length, time, velocity, etc., nonphysical dimensions such as currency are also possible. Accordingly, amounts of money would be instances of PhysicalQuantity. PhysicalQuantities are distinguished from Numbers by the fact that the former are associated with a dimension of measurement
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