Why 3 Subclasses of <Property>?
<Property Value>
Allows you to specify 1 specific <Property>, which can be inherited by the object ‘tree’ rooted at the attributed object.
<Property Description> (used only at organizer level)
For a given <Property>, allows you to qualify it with other <Properties>, e.g. specifying that emissivity applies only to the IR band, the water depth at which temperature measurements were taken.
<Table Property Description>
Used to specify a <Property> being described by a particular element in the cells of a <Data Table>.