View source for OpenSite/Concepts/Properties and units

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A property has more meaning than a displayed number.

== Type, role and validity ==
Quantity properties carry dimension and quantity kind; other types include Boolean, integer, real, text, references and typed lists. An input differs from a derived result. Current, stale and invalid are meaningful states; an old retained number is not automatically current.

== Canonical SI and display ==
The model keeps canonical SI. Display profiles choose how to present it. Entering 300 mm stores 0.3 m. Changing the display to metres must not rescale the object.
[[File:OpenSite_Units_Flow.svg|850px|center]]

== Literal and expression ==
A literal stores a value. An expression stores a source and dependencies, then produces a result. Writing a new literal replaces an expression-bound value through the supported edit path.

== Practical lessons ==
* [[OpenSite/Guides/Quantities and profiles]]
* [[OpenSite/Guides/Native property formulas]]
* [[OpenSite/Guides/Python property expressions]]

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