From http://physics.nist.gov/cuu/Units/introduction.html:
Some useful definitions
A quantity in the general sense is a property ascribed to phenomena, bodies, or substances that
can be quantified for, or assigned to, a particular phenomenon,
body, or substance. Examples are mass and electric charge.A quantity in the particular sense is a quantifiable or assignable property ascribed to a particular
phenomenon, body, or substance. Examples are the mass of the moon
and the electric charge of the proton.A physical quantity is a quantity that can be used in the mathematical equations
of science and technology.A unit is a particular physical quantity, defined and adopted by convention,
with which other particular quantities of the same kind are compared
to express their value.
The concept mass is the <<Quantity>> in the general sense (and will have <<dimension>> Mass), and then the <<ValueProperty>> mass : Mass of the Moon <<Block>> is typed by a Mass <<ValueType>> that represents the Quantity mass with a chosen <<Unit>>.
Visit also:
Similiarly, electric charge is a <<Quantity>> in the general sense, and then q : ElectricCharge is a <<ValueProperty>> of the Proton <<Block>> and is typed by an ElectricCharge <<ValueType>> that represents the <<Quantity>> electric charge with a chosen unit.
