Database Management
Reference Manual
Introduction to Database Concepts
:
Database Attributes
: Attributes of Physical Quantities
Attributes of Physical Quantities
Some real attributes are simply numbers, counts, quantities etc. Others represent real physical quantities such as distances, areas, densities, angles etc. The type of physical quantity is called its physical dimension, often shortened in unambiguous contexts to its dimension. Real attributes (stored, derived, user defined etc.) can all be assigned a physical dimension and this determines the type of data stored in these attributes wherever and whenever they occur in the database. The most common dimensions of attributes are of length (internally set to either DIST or BORE). There are many others supported including density, mass, pressure, temperature, area, volume and angle.
The dimension of an attribute is held in the database in its (ambiguously named) UNIT field. It may be queried directly using the VAR ATTDEF attributeName UNIT syntax, and the !attribute.units() PML ATTRIBUTE object method, refer to
PML ElementType Class
.
1974 to current year.
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