What is System of physical quantities?

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Clarification of Question by ignat-ga on 18 Jan 2005 16:58 PST

This question is not about system of physical units (like SI, SGS and etc.)
I am asking about system of physical quantities which provides
structural scheme of interrelations between different physical
quantities in terms of mathematical expressions given by differential
forms and etc.

A system of physical quantities is a way to describe the "units" of
the universe.  These references refer to SI, a commonly-used
scientific system that uses seven "independent" units.  "All" other
measurements can be stated as a combination of these seven.  (Not sure
if quarks or strings would require a few more units)  Don't forget to
"Always check your units!"

http://www1.bipm.org/en/si/si_brochure/chapter1/1-4.html
In these International Standards, the ISO has adopted a system of
physical quantities based on the seven base quantities corresponding
to the seven base units of the SI, namely: length, mass, time,
electric current, thermodynamic temperature, amount of substance, and
luminous intensity. Other quantities, called derived quantities, are
defined in terms of these seven base quantities; the relationships
between derived quantities and base quantities are expressed by a
system of equations. It is this system of quantities and equations
that is properly used with the SI units.

http://physics.nist.gov/Pubs/SP330/sp330sl.pdf

http://www.profibus.com/cgi-bin/glossary.pl?lang=e&letter=I&id=507&slevel1=TopLevel&slevel2=TechGeneral&sterm=&srange=term